Why not write your own API ? Manual RPC's ? Instead of depending on 3rd party crap ?
Below are a list of most common API's.I don't know the complexity or constants while using them.I'll leave to you to figure it out.
-
https://developers.xapo.com/-https://bitpay.com/bitcoin-payment-gateway-api
-https://gourl.io/bitcoin-payment-gateway-api.html
Additionally, read this reddit post,https://www.reddit.com/r/Bitcoin/comments/46dvrk/best_receive_payments_api/