I had this problem with my 4K Apple TV and Roku. I was trying to use my iPhone when the activation screen appeared. I would sign in on my phone and the activation screen would stay stuck on my tv... but I found a solution. Try using a computer that runs windows and the browser Internet Exploerer, rather than an Apple product (iPhone). Worked for me. It let me sign into the ESPN app and TBS app. I signed in on the windows computer and bam, got the success check on the TV. Hope this helps.
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