This post might help you troubleshoot the issue: Validating compile/runtime configuration - ERROR! the application :backend has a different value set for key :basic_auth during runtime - #2 by wojtekmach
Alternatively, maybe the following from the docs might help (MIME — mime v2.0.5):
After adding the configuration, MIME needs to be recompiled. If you are using mix, it can be done with:
mix deps.clean mime --build
