Port getting blocked when trying to access Webadmin from External

 Hi,

I have configured Dyndns ins Sophos UTM 9.506. I did the port forwarding aswell in the router to access the Webadmin page from external interface (Webadmin Settings>General>Allowed Networks = Any). The ports are open. 

Now, when I try to access the webadmin page, I can get the login page. But, it doesnt take me any further after giving the login credentials. The ports are getting blocked after I click login on the login page. 

Can any one help please?

Thanks in Advance.