The error message "User not authorized for channel" is not generated by Outbank, but by the bank's FinTS server.

The transmission path "HBCI with PIN / TAN" (HBCI +) must be activated on the bank's online banking website ('Services' > 'Online SelfServices' > 'TelefonBanking PIN bestellen und HBCI+ Freischaltung') before the first synchronization.

If this does not help, please contact your bank directly and have your accounts fully activated for the HBCI system or "FinTS with PIN / TAN".