[SOLVED]Impossible for clients to renew their subscriptions by Paypal

Hello,
I have a strange behaviour of CBsubs on membership renewals. Like every year the treasurer of a client association has sent the renewal requests to his members and he called me to tell me that many of them were contacting him to say that Paypal was refusing the payment with the error message "This invoice has already been paid. For more information, contact the merchant".
Have you ever had this happen and if so, can you tell me how to solve the problem?
Thank you in advance for your feedback

When are you seeing that message? When you go to renew from within CBSubs and click the PayPal button?

Checking their documentation it's due to the basket invoice not being unique. Within CBSubs > Settings > Display > Invoices did you change the settings under "Invoice numbering" the defaults guarantee a unique invoice number. The defaults are as follows.

Numbering of invoices: Single invoice number, assigned at ordering time (default)
Invoice number format: [PREFIX_TEXT][NUMBER]
Invoice title format: Invoice [INVOICENUMBER]
Reset next Invoice [NUMBER] to: (empty)
Increment each consecutive Invoice [NUMBER] by: 1

The proforma defaults are as follows.

Proforma Invoice number format: PR-[PREFIX_TEXT][GROWING_ID]
Proforma Invoice title format: Proforma Invoice [INVOICENUMBER]
Invoice number format: [PREFIX_TEXT][NUMBER]
Invoice title format: Invoice [INVOICENUMBER]
Reset next Invoice [NUMBER] to: (empty)
Increment each consecutive Invoice [NUMBER] by: 1

Below can be used to randomly generate a unique invoice each time.

Invoice title format: [PREFIX_TEXT][UNIQ_ID]

Hello Kyle,

He are the settings for this website



So if I understand your message the only thing I have to change is the "Invoice title format" and set it to [PREFIX_TEXT][UNIQ_ID], right?

 So if I understand your message the only thing I have to change is the "Invoice title format" and set it to [PREFIX_TEXT][UNIQ_ID], right?

Correct, that would guarantee a completely unique id every single time.

Thank you for your time Kyle