Best easy to use API option for a travel portal for flight and accommodation? Travelpayouts, Rome2Rio or something else?

Hi Cho
 
Yes, Travelpayouts looks like a nice option. Rome2Rio doesn’t have booking capability. It has search only.
 
If you’re fine with affiliate programs, also check Skyscanner, Allmyles, and KIWI. You may also consider Booking.com and Expedia affiliate programs, but they mostly address accommodation booking.