Your Spring Boot service throws connection errors on startup right after you add the Axon Spring Boot starter. What is the most likely cause, and how would you confirm it?

The most common cause by far is simple ordering: the Spring Boot service started before Axon Server itself was up and healthy, so the gRPC connection on port 8124 that Axon expects to establish at startup fails, producing alarming-looking connection and retry errors in the logs. This does not usually mean your service's own configuration is wrong. The fastest way to confirm it is to open Axon Server's web dashboard at http://localhost:8024 in a browser; if that page doesn't load or shows the server as unhealthy, the fix is to get Axon Server running and confirmed healthy first, then start or restart the Spring Boot service, rather than digging through the service's own axon.axonserver.servers configuration for a bug that likely isn't there.