Who creates a sales order?

The supplier creates the sales order, in its own ERP or order system. The customer creates the purchase order. In EDI the customer's ORDERS message is mapped into the supplier's system as a sales order, keyed to the customer's PO number.

Is a purchase order the same as a sales order?

No. They are two records of one order. The purchase order is the customer's document, under the customer's PO number. The sales order is the supplier's own record of accepting and fulfilling it, under the supplier's own unique number, with the customer's PO number held as a reference.

Which comes first, the purchase order or the sales order?

With a retail customer ordering by EDI, the purchase order comes first. The customer sends its ORDERS message, and the supplier's system turns it into a sales order. SYSPRO's help for its Sales Order Import program, for example, says the customer purchase order number is used as a cross reference to the Sales Order files.

Is a sales order the same as an invoice?

No. The sales order comes first and records what you agreed to supply. The invoice follows the supply and is the VAT document, with its own sequential number. Microsoft's Business Central documentation notes that you cannot create an invoice from the Sales Orders page for something that has not shipped.

Do I send my sales order to the customer?

The sales order is your own record, and Business Central lets you email a copy as a PDF. In EDI, the message the customer receives about its order is the order response, which GS1 defines as a message from a supplier to a buyer responding to a purchase order. Each customer sets whether it requires one.

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What is a sales order? A guide for UK suppliers

How a customer's purchase order becomes a supplier's sales order, which order numbers later EDI messages carry under GS1 EANCOM and Peppol, and five checks to run when an EDI order lands in your ERP.

Transalis2 November 2026

A customer's order arrives under the customer's own number. Your ERP files it under a number of its own. Both describe the same goods, and every document you send afterwards has to keep the two apart.

Key takeaways

A sales order is a supplier's own record of a customer's order that it has accepted to fulfil, created in its ERP or order system under its own unique order number.
The purchase order is the customer's document under the customer's PO number; the sales order holds that PO number as a reference beside the supplier's own number.
GS1's EANCOM standard has no sales order message: the customer's ORDERS message becomes the sales order once it is inside the supplier's system.
GS1's EANCOM order response, despatch advice and invoice each have a code for the buyer's order number (ON) and for the supplier's order number (VN); which ones a customer wants is set in its own message guide.
The invoice follows the supply with its own sequential number, which HMRC requires on a full VAT invoice; the sales order number is not among the details HMRC lists for a VAT invoice.

Short answer

A sales order is a supplier's own record of a customer's order that it has accepted to fulfil. The supplier creates it in its ERP or order system under its own unique order number, and holds the customer's purchase order number on it as a reference. Despatch and the invoice both run from it.

What is a sales order?

GS1's EANCOM standard for EDI has no sales order message. What travels between the two businesses is the customer's ORDERS message, which GS1 describes as "A message specifying details for goods or services ordered under conditions agreed between the seller and the buyer." The sales order is what that order becomes once it is inside the supplier's system.

ERP documentation describes the record from the supplier's side. Business Central documentation from Microsoft treats the sales order as the record that drives delivery: "When you post a sales order, you create a shipment and an invoice." Sage 200 Professional help gives each sales order two numbers, the supplier's own and the customer's (more on both below).

Some suppliers also send the customer a copy; Business Central's documentation notes that "When you post the sales order, you can also email it as a PDF attachment." In EDI, the message the customer receives about its order is the order response, covered below.

Sales order vs purchase order: what is the difference?

One order, two records. The purchase order is the customer's document; the sales order is yours.

	Purchase order	Sales order
Who creates it	Your customer	You
Whose number it carries	The customer's PO number	Your own unique order number, with the customer's PO number held as a reference
Where it lives	Your customer's buying system	Your ERP or order system
What it starts	The instruction to supply	Picking and despatch, then the despatch advice (ASN) and the invoice
In GS1 EANCOM	The ORDERS message, numbered by the buyer	No message of its own; your number has a place on later messages as "VN = Order number (supplier)"
Quoted back later	On the documents you send the customer	Where your customer's message guide asks for it

The purchase order guide covers the customer's side: "A purchase order is the customer’s instruction to supply: which products, how many, where to deliver and when, under the customer’s own PO number."

What is a sales order number, and how does it relate to the PO number?

A sales order number is the supplier's own unique number for the order. The customer's PO number sits on the same record as a reference.

Sage UK's help for Sage 200 Professional shows both fields on one screen. For the supplier's number, its help page on confirming a sales order says: "This must be a unique number." For the customer's order number field: "This can be a reference that the customer gives you, their name, or their own order number."

The EDI standards keep the two numbers apart too. GS1 lists a code for each on the EANCOM order response, despatch advice and invoice.

Number	Who issues it	Where it travels
Customer's PO number	The customer	The ORDERS message; on later EANCOM messages as "ON = Order number (buyer)"; Peppol BT-13
Your sales order number	You	Your ERP; on later EANCOM messages as "VN = Order number (supplier)"; Peppol BT-14, optional
Invoice number	You	The BGM segment of the EANCOM invoice message; Peppol BT-1. A credit note can quote it back as "IV = Invoice number"

On the order response, GS1's note for the reference segment says: "This segment is used to refer to the Purchase Order or Purchase Order Change Request to which the Purchase Order Response is responding." The customer's number is the one the response answers. Your own number has a slot beside it, and whether a customer wants it filled is set in that customer's own message guide.

The Peppol e-invoice standard says who issues each number. The purchase order reference, BT-13, is "An identifier of a referenced purchase order, issued by the Buyer." and the sales order reference, BT-14, is "An identifier of a referenced sales order, issued by the Seller."

The invoice number is a third number again. HMRC requires a full VAT invoice to show "a sequential number based on one or more series which uniquely identifies the document". HMRC sets rules for the invoice number, not the sales order number. The invoice number guide covers those rules.

How does an EDI order become a sales order?

The order arrives. The customer sends an ORDERS message. Its document number is the "Order Number assigned by document sender", which is the customer's PO number.
The order is mapped. Translation turns the customer's format into the one your system reads. As the EDI mapping guide puts it: "The map moves each value into the right field in your system."
Each line finds its product. An order line can carry more than one product code, and the SKU guide explains that "your system has to know which is which before it can act on the order."
The sales order is created in your ERP, keyed to the customer's PO number.
You respond, if asked. Where the customer requires it, you send an order response pointing back at its order.
You pack and despatch. The despatch advice (ASN) follows: in GS1's words, "A message specifying details for goods despatched or ready for despatch under agreed conditions."
You invoice, quoting the customer's order number, and your own where the customer asks.

SYSPRO's help for its Sales Order Import program shows step 4 in one ERP. The program is used "to import an order file transmitted from a customer designated as an EDI trading partner." Its file layout makes the customer's number the key: "The customer purchase order number must be unique as it is used as a cross reference to the Sales Order files." A separate field for the actual sales order number is marked "Used by confirmations only."

The Transalis Dynamics 365 EDI guide describes the same step in its own words: "A customer’s purchase order arrives in its own format and reaches the ERP as a sales order in the structure the ERP expects."

The ASN guide picks up from there: "the supplier confirms it, then picks and packs the goods against that confirmed order."

Not every order lands straight in an ERP. The web EDI guide draws the line: "With web EDI a person reads each order and keys each invoice, while integrated EDI connects an ERP, accounting or warehouse system so documents flow without rekeying." A web EDI supplier with its own ERP keys each order in as a sales order by hand.

Sales order vs order response, invoice and pro forma invoice

Order response. The sales order is the record inside your system. The order response is the message you send the customer about its order. GS1 defines the EANCOM order response as "A message from a supplier to a buyer, responding to a Purchase Order message or a Purchase Order Change Request message." The purchase order guide's section on the order response (order acknowledgement) covers what a response can say and when customers require one.

Invoice. The sales order comes first and records what you agreed to supply. The invoice follows the supply and is the VAT document, with its own sequential number. Business Central's documentation puts the order plainly: "Note that you cannot create an invoice from the Sales Orders page for something that has not shipped." HMRC's electronic invoicing notice (VAT Notice 700/63) gives an example of a system control: "a control which prevents a sales order being changed after the invoice has been issued". If the value goes up after invoicing, the debit note guide covers the document that records the change.

Pro forma invoice. Not a VAT invoice. HMRC says pro formas should be "clearly marked ‘this is not a VAT invoice’", and that "Pro-forma invoices are often used to offer goods or services to potential customers."

What to check when a customer's order becomes your sales order

The checks are our advice; the rules behind them are GS1's and your customers' own.

Hold the customer's PO number on the sales order, exactly as sent. GS1's order change message cannot alter it: "A change may not be requested on the Purchase Order number, the identification of buyer and seller, or the line item number." That makes it a stable key.
Resolve every order line to your own product code before you accept the order.
Send an order response if your customer requires one, pointing at the customer's order number.
Apply each change from the customer to the same sales order, and check it before you despatch. The customer measures delivery against its own order. As the OTIF guide says: "The customer scores OTIF from its own goods receipt against its order".
Quote the customer's PO number on the despatch advice and the invoice, and your own order number as well where the customer's guide asks for it.

How Transalis gets customer orders into your ERP

Transalis is a managed outcomes provider for B2B integration, EDI and eInvoicing. Its EDI page names the job a sales order team knows well: "Rekeying orders from PDFs and emails into your ERP by hand." Integrated EDI takes that step away, so the customer's order lands in your ERP as a sales order, as the Dynamics 365 guide above describes.

For suppliers on SYSPRO, the SYSPRO EDI integration page states the offer: "Connect SYSPRO to your trading partners with fully managed EDI from Transalis". Suppliers not ready to connect an ERP can follow the EDI page's own path: "Start in a browser and grow into your ERP when you’re ready."

Map your supply chain from your customers' orders to your sales orders.

Frequently asked questions

Who creates a sales order?: The supplier creates the sales order, in its own ERP or order system. The customer creates the purchase order. In EDI the customer's ORDERS message is mapped into the supplier's system as a sales order, keyed to the customer's PO number.
Is a purchase order the same as a sales order?: No. They are two records of one order. The purchase order is the customer's document, under the customer's PO number. The sales order is the supplier's own record of accepting and fulfilling it, under the supplier's own unique number, with the customer's PO number held as a reference.
Which comes first, the purchase order or the sales order?: With a retail customer ordering by EDI, the purchase order comes first. The customer sends its ORDERS message, and the supplier's system turns it into a sales order. SYSPRO's help for its Sales Order Import program, for example, says the customer purchase order number is used as a cross reference to the Sales Order files.
Is a sales order the same as an invoice?: No. The sales order comes first and records what you agreed to supply. The invoice follows the supply and is the VAT document, with its own sequential number. Microsoft's Business Central documentation notes that you cannot create an invoice from the Sales Orders page for something that has not shipped.
What is a sales order number?: It is the supplier's own unique number for the order, set in its ERP. In the GS1 EANCOM standard it is the order number (supplier), qualifier VN, and in Peppol it is the sales order reference, BT-14, issued by the seller. The customer's PO number is a separate number.
Do I send my sales order to the customer?: The sales order is your own record, and Business Central lets you email a copy as a PDF. In EDI, the message the customer receives about its order is the order response, which GS1 defines as a message from a supplier to a buyer responding to a purchase order. Each customer sets whether it requires one.

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