An environment is configured with the RACF option PASSWORD(NOMIXEDCASE) – “MIXED CASE PASSWORD SUPPORT IS NOT IN EFFECT” specified. 

If a user attempts to login from any off-mainframe interface (e.g. the REST Services API web app, the Client Pack UIs (ZDD or ZMF4ECL), etc.) with a lower or mixed-case RACF password phrase, which is always case sensitive despite the above option, rather than a password they fail with the following type of error message:

ICH408I USER(USER001 ) GROUP(SUPPORT ) NAME(SUPPORT USER       )
  LOGON/JOB INITIATION - PASS PHRASE IS NOT VALID                

Problem originally reported for the REST Services API web app running against an 8.2 Patch 5 ZMF Server environment.

Full article: https://portal.microfocus.com/s/article/KM000014053