Hi there, @poll-park.

I can see you've tried all the necessary steps to get this pay now button working. I can help provide additional details about this.

As long as your PayPal App is enabled and you've performed all the steps provided by my colleagues, you should be able to use the pay now button option. Since we don't have any reported investigation regarding this issue, I'd suggest reaching out to our Online Specialist to check this further.

They have extra tools that will help isolate this unusual behavior in QuickBooks.

Should you need other references for future use, you can visit our help site for more information. 

Let me know if you have other questions about the pay now button. I'm here to help.