Check the logs
Check the log files inside
logs/ in the agent installation folder for logs and
errors. The resolver logs a line for each credential ID that it successfully
queries, and also logs the fields that the credentials were extracted from.
If a particular credential ID is failing, search for that ID in the logs, and check that it is successfully queried and that the credentials were extracted from the fields you expected.
You will also find any exceptions that the resolver throws in the logs, including if it didn't find the minimum set of required fields as specified in configuration, or if it couldn't communicate with Vault.
Use the Test credential feature
When creating or configuring a credential in the ServiceNow UI, you should be able to click "Test credential" to perform a quick targeted test. Select the MID server that should query Vault, and select a target that the credential should work for to check that everything works as expected. If it doesn't, check the logs for errors and debug information as detailed above.