Hello efarmer,

Thanks for reaching out to us here in Community.

If you are wondering why you keep on getting this error, you can try to update QuickBooks Desktop to the latest release.

Since you're running QuickBooks 2015, you need to be at least on release 6 or higher to let the customer pay online. You can click Help> Update QuickBooks and install any available updates Quickbooks 2016 has the ability to e-invoice from R1 and up.

When creating the invoice, you need to make sure to enable it for online payment. This can be done in the preferences as well under the Payments option.

You can check out this article for more information: “View and Pay Invoice” button missing when emailing e-invoices from QuickBooks 2015 and 2016?

Feel free to leave a comment if you need anything else.