not receiving email with voucher link – continued

Hi, I noticed you had an earlier post about clients not receiving emailed vouchers. A user had suggested updating the headers in wp_mail function of voucherpress.php

I can’t find wp_mail function in voucherpress.php. Can you advise where it is?
If not, what is the solution to ensure every client receive an email?

Winston
https://www.b-soho.co.uk

https://www.ads-software.com/plugins/voucherpress/