Electronic Payment Web Implementation

Hi. I’m trying to develop a reactive web.

It’s similar to electronic payment, but in one form, two people exchange it.

I’d like to create a web that can be added as below.

For example, A writes the contents and sends it to B.

B will add the amount and send it to A again.

Check if A is correct (check box) and send it to B again. (The final modification is made here and cannot be modified anymore.)

I don’t know what language to use or how to implement the ability to send it back and forth.

I don’t have a clue. Please give me some advice.