SQL Server 2017 Availability group not routing to secondary server
2 more things to be noted here while you are trying to connect to the Listener via the Management Studio for ReadOnly routing:


Make sure that you are also providing the database Name along with "ApplicationIntent=ReadOnly" in the Additional Connection parameters section of SSMS
SSMS sometimes has sticky connections so it could be possible that it is still connecting to an existing connection that was made via SSMS before providing the parameters "ApplicationIntent=ReadOnly". Try restarting the SSMS.