The message is going to incorrect GenServer, which is the reason for the function clause error.
Exq.Mock.start_link(mode: :fake)
Inspect the return value and if it is {:error, {:already_started, #PID<...>}}, then the issue is due to the incorrect name in the config.
config :exq,
name: Exq.Mock,
Exq.Mock is used by mock server by default, so you can’t use that name elsewhere. Change it to Exq and it might fix your issue.
