How to set email send receipt when pending status

Are you comfortable with custom PHP development?

Yes.

Great, and are you familiar with how the add_action() function works in WordPress?

Yup

Sorry, it seems I missed your reply. Are you still needing help with this?

yes, of course. In the end I decided to create its own payment gateway based guide on your website.

However I have a problem. I created a form containing a message instruction in the settings automatically sent when the customer presses a button purchase. But I have not succeeded.

Can you help me?

here is my code

https://pastebin.com/qjTE2UHH

this is a screenshot

https://prntscr.com/2x3y8w

Can you help me how to write a email function for this?

Thanks,

Could you make the paste non-private so I can see it?

oh sorry, see here

https://gist.github.com/rephseven/9315763