AMC fail. I just submitted a ticket with the same problem. These companies do a poor job of app rollouts. You'd think with all the money they make they would hire some decent programmers and test everything first.
The reply I received for same problem from AMC Plus
We apologize again for the trouble you're having with this. Our tech team is working to have this resolved as soon as possible―hopefully within a day or so. For now, if it's possible for you to use another device, please do so.
We regret for the inconvenience and thank you for your patience as we try to sort this out.
I also took easy way out. I just activated AMC Plus from within AppleTV until this mess gets sorted out. I feel taken for a ride by AMC by signing on for a whole year. Now I’m basically captive and haven’t heard any talk of refunds or ways out. Will turn off the AppleTV version once the standalone Roku app is fixed, but will have ended up paying more. Looking forward to the end of my contract in standalone app. AMC Plus looks and behaves much better from within the AppleTV app.
I canceled my AMC Plus subscription today (11/24/2021). Looks like I am going to be out of the yearly subscription I did directly with AMC. I activated AMC Plus on the Roku channel and it is playing fine. DO NOT subscribe directly from AMC.
After switching out various streaming devices so I could watch AMC Plus in the living room, this morning I bit the bullet and made one last ditch effort to fine a solution to AMC Plus not being playable on Roku Ultra. This is what worked for me.
I did a Factory Reset on the Roku Ultra, which basically is like taking it out of the box for the very first time.
Factory Reset which requires reactivating the Roku Ultra, getting an email, entering a code, etc.
Pairing remote to your TV.
The final step necessitated entering my identity (email address) and password for half of our premium streaming channels. I started with "the problem child" AMC Plus to verify that this corrected the issue, before I wasted a lot of time signing back into the rest of the channels. It did.
Don't ask me how or why, but some of the streaming channels seemed to remember my credentials and didn't require me to sign in again. Others I had to do all over again.
Thanks, and you deserve kudos for the fix but... that is a lot of hassle and inconvenience for an app that does not work that we have paid for. We basically paid for something that did not exist and they are still advertising it as available on Roku despite all these issues. It's basically take the money first, work out the issues later. They know there is an issue and are still selling the product. They either send canned replies or say they are working on it. Are they working on adjusting the sales ad?