Captive sign in WiFi message on my mobile

[gemini49]

My connection has been dodgy for days through my mobile (using apple phone) and today I have a message pop up "Log in to captive WiFi" asking for username and password.  
I have googled how to disable it but am unable to find where to do this.

has anybody come across this problem?

[JudgeB]

Did you found a way?  I had  sky hub max rellaced and same issue came back after 24 hours.

i can connect directly through ethernet port but  apple deviced, my lg smart tv, alexa,  amazon fire tablet do not connects and requesting for captive login which comes up as router gateway login. I tried everything what i could find on internet and nothing works 

i can not find any set up in the router setting which would be resposible for this captive option.