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.
I don't believe all of your information is correct. The Spectrum App will work even if not connected to Spectrum provided Internet, just not have access to all the programming. I can also log in to SpectrumTV.com and access TV content. However, when I'm away from my In-Home Spectrum WiFi, there are programming restrictions.
From the Spectrum Web site : "Note: Please download the latest version of the Spectrum TV app. Allow at least 24 to 72 hours after creating your Spectrum.net username before you sign into any TV apps. Programming will vary based on whether or not you’re connected to your In-Home WiFi. The Spectrum TV app will not work internationally."
Is it perhaps possible the issue is on the ROKU side, seeing that I can use my credentials to log in over the web, but not the app?
Thanks for letting us know about the issue that you are experiencing.
You'll need to get in touch with Spectrum support and have them assist you with your account/service. They can help walk you through logging into their channel on the Roku platform. If you encounter any errors such as you described, they will need to investigate what may be causing them within your account. Roku doesn't have any control over authentication credentials for 3rd party channels—the channel provider will be the point of contact for resolving those types of issues.
Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more.
If the issue remains unresolved, I'd recommend reaching out to Spectrum directly to report the issue and request additional support. Many channels on the Roku platform is developed and maintained by the channel provider directly, and they'll be able to best assist.