LNK Numbering and References: your invoice, credit slip and delivery slip numbers, and the customer's purchase order number

At the top of the Payment step of the checkout, before choosing the payment method. What they type is saved as they go; the customer sees "Saved." under the field.

Yes. Tick the customer groups concerned in the settings. These customers cannot pay without a reference; the others see an optional field. The group that counts is the customer's default group.

Not through the checkout. The payment button waits for the reference, and if a payment is started without it, the server sends the customer back to the Payment step with a message, before the order is created. One limit only: a payment confirmed outside the checkout, by a server-to-server call from a payment provider (without the visitor's cart), is not checked. The order is then created without a reference, and you can add it from the order page.

Yes, on the PDF invoice and delivery slip, under the order details, with the field label in the language of the order. A switch in the settings removes it from both documents.

In the back office order list, the "Customer ref." column has its filter: type all or part of the number. The search covers every order, not only the page displayed.

Yes, from the order page in the back office, by an employee allowed to edit orders. An empty field removes the reference.

Yes. The order e-mails (confirmation, status changes) receive the {lnk_poref} variable. The module changes no e-mail template: add the variable wherever you want in your templates. It is empty when the order has no reference.

Letters and digits of every script, spaces and . , _ / # : + -, with a letter or a digit first. The maximum length is a setting, 40 characters by default and 64 at most. A refused entry shows a message under the field.

Yes, in each language: "Purchase order number" or "PO number", for example. Left empty, the field keeps "Your order reference", translated. The same label is used in the order details and on the documents.

No. The module loads 0.5 KB of CSS and 1.3 KB of JavaScript, compressed, on the checkout page only. The other pages load nothing.

With PrestaShop's native checkout, without any setting (checked with Classic on 1.7.6, 8.1 and 9.2). A custom theme or checkout places the displayLnkPorefField hook; the server guard applies either way.

Yes. Settings are made per shop, per shop group or for all shops. Each reference is tied to the shop of its order. Numbering series are set shop by shop, each with its own counter.

In the settings, Numbering section, open Invoices. Write the pattern, for example F{YYYY}-{NNNNN}, choose when the counter starts again (never, every year, every month), then switch the series on. The preview shows the next number as you type. Orders, credit slips and delivery slips each have their own series, on the same model.

They keep their number: the module never renumbers an issued document. The series only applies to the next documents, and its suggested start is just above PrestaShop's last number, so that no printed number comes back.

No. The counter is taken in a single query that locks its row, and a unique index refuses any duplicate. Two documents issued together get two numbers that follow each other.

Yes. The PDF credit slip carries its series number as title and file name, and a line quotes the original invoice with its number and date, in the language of the order.

Yes. The numbers already given stay as they are, and the new pattern applies to the next documents. A number already given is never given again. The journal keeps every change, with the employee and the date.

It uses the core hooks wherever they exist. For the title and file name of the PDF credit slip and delivery slip, the core offers none that works: the module installs two declared overrides, and a third one for the order reference on 1.7.6 to 8.0. PrestaShop installs and removes them with the module. No e-mail template is changed.