Hi,
(1) All machines with Availability Groups must have the Service Broker endpoint exists and correctly configured. Use the following query to confirm you have Service Broker endpoint:
SELECT name, protocol_desc, type_desc, state_desc, port
FROM sys.tcp_endpoints
WHERE type_desc = 'SERVICE_BROKER';
Go over the following document: https://learn.microsoft.com/en-us/sql/database-engine/availability-groups/windows/service-broker-with-always-on-availability-groups-sql-server?view=sql-server-ver15&WT.mc_id=DP-MVP-5001699
In most cases, you simply need to CREATE ENDPOINT
(2) If the above did not solve your issue then please check what is the exact version of he server (please check @@VERSION)