Pay Now Button Does not Appear in Client Portal

I recently upgraded from v4, and have found that the Pay Now button does not appear on the screen located at (myurl)/client/invoices/payment.
The clients can click the first pay now button, but once landing on the link above have no option to pay.
I have the Stripe and Paypal Gateways configured and enabled.
I also have tried deleting and reconfiguring those gateways.
I am using version v5.1.74-C51

Any advice would be much appreciated.


@david @ben any thoughts to debug this?

I ended up solving the issue by installing another copy of v5 and importing data via csv files.
I did have to recreate all recurring invoices and settings manually, but that ended up being the fastest solution.