I was able to resolve the issue.
The problem is for those that are migrating from another att video service, e.g. DIRECTV satellite and that account was linked to myATT. If you used the same email as the myATT login or the same email as your previous video service, the Roku app will not work even though other apps (iPhone or Apple TV) work just fine.
the solution is to open a new DIRECTV Stream account with an unrelated email and DO NOT LINK this account to myATT. Note when ordering a new DIRECTV Stream service there is an option to use a previous ATT email - DO NOT USE. Set up DIRECTV Stream as if you have ZERO relationships with ATT.
I then had to call ATT and cancel the previous account (i.e. the one that was linked to myATT and that used the same email as DIRECTV satellite) that wasn’t working on the Roku device
This is what I did and it worked for me.