Note: This currently only works for PayPal.
PayPal also balks if they try to use a PayPal account with different email. I got so many support calls, where the link did not work that I quit using it. This would help a LOT with actually getting paid. Clients hate logging in to yet another system (our Clientexec) to pay invoices. Many clients just call me to pay their invoices, I view as them and enter their info that they give me over the phone. Lot of wasted time to collect payments.
It would be nice if it worked for all credit cards, or at least for Stripe, Square, etc.