Problem with creating new websites ISPConfig 3.1.10 Debian 9 after ispconfig_migrate tool

Hi,
I have setup a virtual test server in order to check that the migration tool is going to work properly and to doublecheck if my setup is going to be working without errors, before changing my current production server running Debian 8 to a new server running Debian 9.
However, after using the migration script (everything went smoothly) I cannot seem to be able to create a new website. When I start the new website creation the back office does not allow me to type the new domain but restricts me to using any of the previously setup domains.
I don't know if this has been caused by an incorrect update of ispconfig or if it has been an error of the migration tool but this is something that is troubling me a lot.
Any chance that anyone has any input on this as I was planning to retire the old server over the coming weekend and I want to be absolutely sure that everything works as it should.
Thanks,

Nikos