Originally Posted by download

Unfortunately I'm getting the exact same issue as you. Tried both Chrome and Safari, and splitting the payment with a credit card. Neither worked.

Using only TravelBank it would spin forever, splitting with card it would immediately show this message:

We're unable to complete your request.

We’re unable to process this transaction due to an issue with your credit or debit card company. Please try again with another form of payment or contact your credit or debit card company for more details.

I had the exact same issue back in January and somehow found some hack to finally get a couple flights to process, but I'm blanking on why. It's ridiculous that it's been two months and United still hasn't fixed it.