Thank you very much for your help

1. Go to Settings > Technical > Sequences & Identifiers > Sequences.
2. Find the sequence used for generating FPOS invoice numbers. It might be named "Account Invoice - Sales - FPOS".
3. Edit the sequence record.
4. In the Numbering section:
   • Set Number base to Custom.
   • Enter the desired prefix in the Prefix field (e.g., "FPOS ").
   • Set Number padding to the desired number of digits (e.g., 5 for 5-digit numbers).
   • Leave the Number Increment field as 1.
5. Click Save.

Hi,

Here are the general steps to modify the billing sequence:

1. Go to Settings: Log in to your Odoo instance and navigate to the "Settings" module.
2. Technical Settings: In the Settings module, make sure you have enabled the "Developer Mode" (you can find it at the bottom of the settings page).
3. Customization: After enabling Developer Mode, you will see additional options and menus. Go to the "Technical" menu.
4. Sequences: Look for the "Sequences & Identifiers" section. Under this section, you'll find "Sequences."
5. Find or Create Sequence: Find the sequence related to your POS invoices or create a new one. Sequences in Odoo control the numbering for various documents, including invoices.
6. Edit Sequence: Once you find the sequence you want to modify (like the one used for POS invoices), click on it to open the sequence form.
7. Modify the Sequence: In the sequence form, you should see a field for "Prefix" and another for "Number Next." Update the "Prefix" to your desired prefix (like "FPOS") and set the "Number Next" to the starting number you want (like 50685).
8. Save Changes: After making the necessary changes, save the sequence.
9. Test: Go back to the POS and create a new invoice to see if the changes take effect.

Hope it helps