Even though you will save space by combining both fields onto a single page, I would be inclined to present each field on it's own screen.
The user elects to pay
The user is prompted for password - the user enters password
The user is prompted for OTP
This way each page could have it's own intro text and help links if required. Otherwise you would need to include a 'forgot password' link and a 'resend OTP' link all on the same page, feels cluttered.
Have a nice animation linking the screens together if possible to ensure a feeling of consistency between the two steps.
Maybe have some light hearted text like, 'just one more step...' on the OTP page or something to smooth over the extra effort required.