i have a problem with SSTP Client on Mikrotik Router OS 7.6
When I create a connection SSTP Client in version 7.6, there is a problem and not connecting
But this problem does not exist in version 6.49
In version 7.6, it shows a connection error "Closed by Peer Remote"
Try downgrading to 7.5. I have same situation. Works perfectly any v6.x and won't work 7.6 and 7.7b10. I downgraded to 7.5 and it works.
I have a ticket open with mikrotik. Let me know if that works for you. Turning on debug logging was useless. Its disconnecting the server end with the same error you are getting.