HIi,
Give a discount only once per customer, ideally on their first purchase.

Step 1: Create a "Welcome Discount" Product

1. Go to Sales > Products.
2. Create a new product:
   • Name: Welcome Discount
   • Product Type: Service
   • Can be Sold: ✅
   • Price: -100.00 (or any discount value)
   • Available in POS: ✅

Step 2: Use a Customer Tag or Internal Note

1. Go to Sales > Customers.
2. Add a custom tag or set an internal note on the customer (e.g., "Eligible for Welcome Discount").
   • This will help your POS staff identify if the customer is new or has not used the discount yet.

Step 3: Train POS Staff on the Flow

1. When a customer registers via your form:
   • Create the customer in Odoo.
   • Add the tag or internal note.
2. When the customer comes to POS:
   • The staff searches for the customer.
   • Checks if the customer is marked as eligible.
   • Adds the Welcome Discount product manually to the order.
   • After payment, remove the tag or update the internal note.

i hope it is usefull