7. Error - This invoice has already been paid
This page will explain why the error "This invoice has already been paid" happens and how to fix this error.
"This invoice has already been paid. For more information, please contact merchant.".
If you own multiple online stores and want you want to use one Paypal account to collect sales, then you will need to configure "allow invoice duplication", otherwise you may encounter following errors.
"This invoice has been paid. For more information, please contact merchant."
Why this error will happen?
Paypal has function to block duplication invoice, by default, this function is on.
So when your customer try to perform payment from different store, the invoice ID might be has been used from another store. So the error will be displayed.
If you are using Agile Seller Comission module, this error may also happen when you try to pay sellers or seller try to pay you.
This can be fixed by changing one setting from within Paypal, so log in to your Paypal account do the following:
1. Click "Profile" on the top menu bar.
2. Click "My Selling Tools Preferences"
3. Look for "Block payments" and Click "Update"
4. Under "Block Accidental Payments", choose "No, allow multiple payments per invoice ID".
After this setting, the issue should be fixed.