How to just send that from application to anoher website

Hey Everyone
Hope Everyone is doing good!

Overview:
I am making an application in which I had to implement cashmaal payment gateway I had created a php Script with which users will submit their transaction details to cashmaal and then I will recieve the payment.


Problem:

I want that user just enter his data on the application without using a webviewer (I mean in backend) and when the transaction succesful then just continue whatever it is.

in short
when the user posted data there are types of payment method available in the api which I am using. when he/she filled the form then just by backend I want that data has to be sent and everything.

I know that I am having a bad English but If someone is just understanding me a little please help me

Short answer, use post method.