This invoice has already been paid. For more information, please contact the merchant.

[gstricklind]

It seems most donations are going through, but some are redirected to the page with the following error: This invoice has already been paid. For more information, please contact the merchant.

I have no idea what this could be? Any help is appreciated. Thank you!

[donsmithri]

This suddenly started happening to me, too today (in the sandbox).  not predictable.