Exception:

java.lang.IllegalArgumentException: User doesn't have access to use agent

Resolution:

User doesn’t have access to use agent Salesforce Exception occurs when you try to create Agentforce Agent in Salesforce with incorrect Agent User type.

User License should be Einstein Agent for the Agent User while configuring the Salesforce Agentforce agent. You can select New Agent User if you don’t have any user with the User License as Einstein Agent.