At this address: https://developer.exactpay.com/docs/authentication
It says to send a email to implementations@exactpay.com
I did it buy the email bounced:
550 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient’s email address for typos or unnecessary spaces.
Thanks for spotting that. It’s a typo; the correct address is implementation@exactpay.com