After login, user sees error message on Matrix42 Pro/IGA login screen “Access denied when authenticating with …”
 

See keycloak.log and search with this text: 
Redirection URL contains an error
See that founded log message timestamp matches to failed login attempt.

keycloak.log can be opened from Pro/IGA admin page, under Connectors / Logs / esa logs 

Example of error message:
2026-05-20 10:18:30,486 ERROR [org.keycloak.broker.oidc.AbstractOAuth2IdentityProvider] (executor-thread-103) Redirection URL contains an error. providerId=keycloak-signicat-oidc, redirectionUrl=https://customer1.fi/auth/realms/passu/broker/keycloak-signicat-oidc/endpoint?error=access_denied&error_description=The+Resource+Owner+did+not+complete+the+login.+urn%3Asignicat%3Aerror%3Ainternal%3B+Internal+system+error&state=3hO7UgL1UBF4CUzYN8dpcj26Zk4rLhZ2hFbfgiXV0mE.G2_-If5-o6w.Pt_2IbgsS0mRIVLrJWAprw

This means usually that there is some technical issue on Signicat side. These issues can in many cases affect all customers using same Signicat related login method: Bank login, suomi.fi login or sms-otp use-cases.

Action to fix situation: Connect Matrix42 servicedesk and ask them to create ticket for Signicat related to this customer which is having login issue. Give them also error message you found from logs.