To send the actual mail with sendmail, i have stolen the code from
go-mail[0] and removed everything i did not need. This is because there
is no Go package to send email in Debian 12, and this was easier than
to build the DEB for go-mail.
Once i have the time….
[0]: https://go-mail.dev/
I have to basically do the reverse of signing the request to verify that
the notification comes from them. Lots of code just for that.
I return the changed status from the PL/pgSQL function because i will
need to email customers when a payment is completed, and i need to know
when.