Nope, not RESTful but still looks usable and they would surely iterate and improve. Violates third, fourth and last of Roy Fieldings constraints [1], last one being really helpful while using APIs [2]

[1] http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hyperte...

[2] https://en.wikipedia.org/wiki/HATEOAS

Cashfree looks promising and something really needed in India especially the bank transfer API. Good luck to the team.