RBR860 Allowable Website

My question is where do I check in my router to determine whether it is blocking access to a specific website.  Or, is there a place in the RBR860 where I can enter a website such as http://blahblahblah.com  

where I can be assured traffic will not be blocked.

 

Here's the issue: I am trying to subscribe to a Firestick server. But upon entering my Login credentials, I immediately receive a response that says, "Please check your server, Login ID or Password", in other words, it immediately blocks my login attempt.

 

In speaking with the content provider, they assure me my credentials are correct and that I must have a firewall or other security issue that's preventing me from accessing their site.  I am able to access other media content providers like Netflix, Paramount+, etc. on this same network without an issue.

 

Any ideas what I might want to try that will determine if the problem is on my end?

TIA

Jim