Does the issue only occur on Spotify or across other channels installed on your Roku device?
Have you tried removing the affected channel Spotify and then re-install again? If not, we suggest starting there. In some cases, removing the affected channel and then re-installing it may help. Restart your device before re-adding the channel back in to ensure the process is successful. We recommend doing this through the Settings menu by navigating to Settings > System > Power (If there is no Power submenu, proceed to the next step.) > System restart.
In that case, It's best to reach out directly to get the channel going on your Roku. They can resolve the error you are having with the channel login. Please be noted that Roku doesn't manage channel logins or authentication and many channels on Roku are developed and maintained by the channel provider themselves.