Hello,

Try these steps,

1. Check if the partner exists,
   • Go to Settings > Technical > Database Structure > Records
   • Search for "res.partner" model and ID 8
   • If it doesn't exist, you'll need to fix the reference
2. Find where the reference is being used,
   • First check your POS configuration,
     • Go to Point of Sale > Configuration > Point of Sale
     • Check if any POS has a default customer set (that might be the missing customer)
3. Fix the reference,
4. • Through the Odoo interface,
     • Go to Settings > Technical > Database Structure > Models
     • Find the 'pos.config' model
     • Open records and locate the configuration that's using partner ID 8
     • Change the reference to a valid partner
5. If you don't have technical access,
   • Create a new customer with the same information
   • Contact Odoo support to help update the references in the database

After fixing the reference, clear your browser cache and try opening the POS session again.

Hope this helps.