We are still running FM server 12 but someone wants me to host a database created with FMP 13 and there doesn't seem to be a way to enable IWP access for it. Or at least, I don't know enough to find it.
Is it because there are no iwp extended privileges on FMP 13? Is there a way to "downgrade" the file in order to be able to enable IWP access?
In Manage > Security on the Extended Privileges Tab there is still a listing for the fmiwp privilege. You should simply need to assign one or more privilege sets to that privilege. Worked for me.
Keep in mind that if some features new to 13 were used in the development of this solution, they will not work properly when accessed with 12.