It goes through the whole process but it does not complete the transaction.
I would expect that coming back to the site after approving payment with paypal that there would be a final button to press to actually pay... but there isn't so the payment is left as "invoice-checkout" rather than "invoice-paid". There needs to be a button to approve final payment.
In the transaction tab the message column reads "The payment is pending. See pending_reason for more information."
Tested in sandbox.
This is the vanilla Paypal plugin with non-recurring payment.
This is a fresh install of latest version of payplans.
This ticket is marked as high priority because non-recurring payal payment cannot be accepted in this state.