Well, the topic is old, and the protocol is legacy, but someone should still use it as, even if it’s just for tshoot, well I had the same problem trying to connect a windows client to a pptp srv.
In this Microsoft community link, https://support.microsoft.com/pt-br/help/923944/list-of-error-codes-that-you-may-receive-when-you-try-to-make-a-dial-u In this Microsoft community link, it says that error 628 is that the port has been disconnected.
Well in some searches, I found it could be something about encryption, it was the one where I veiriquei in my SRV VPN in profiles in the protocols tab, the encryption option was not checked, and in the configuration properties of the ppp interface in the MS client was selected, the option if you do not have encryption disconnect.
in this case to test I enabled the encryption and works perfectly, but has options where you can choose to keep connected if it has or not encryption.
This error occurred in Win 7, already in Win 10, I did not have this problem.