Guest Express Checkout flow works in both sandbox and production but regular check out hangs after prompting for login. I have created a ticket with Paypal Technical Support. I also gave them credentials to the system so they can see the error occurring, but they have yet to offer any solutions. Since I have already lost hope on this ever being resolved via support, I completed a different integration that actually works and does not use those javascript rendered buttons. It relies on the "approval_url" that is supplied when a billing agreement is created. What I do is launch my own pop window, control its state as much as possible to emulate what the "PayPal buttons" used to do. Using this technique, everything works and I don't have to rely on any javascript libraries.
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