Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
My Acorn subscription is directly with Acorn so I don't know the answer for sure, but I think in order to use Acorn's own app you have to have an account directly with them.
When I sign out of my Acorn app, then sign back in, I am given the choice of starting a new subscription or signing into an existing one. When I sign in, I'm not given the option of signing in via a third party subscription but I have to enter my Acorn email and password.
If you really want to use the Acorn app, I'd suggest you UNsubscribe from your Acorn sub thru the Roku channel to keep it from auto-renewing when your current subscription expires. When it does expire, then install the Acorn app and take out a new subscription directly.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi LivRm - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi BedRm - JVC EM37T
Roku 3, 4200X, Ser 4124C7087583, wifi GstRm - Sanyo DP26640