503: Max Client Queue and Topic Endpoint Flow Exceeded

The number of "flows" is, roughly speaking, the number of endpoints to which you are subscribed. There are two types: ingress (for messages from your application into Solace) and egress (for messages from Solace into your application). You violated one of those limits. You can tell which by looking at the stack trace.

By default the limit on flows is 100. Before you increase this limit, ask yourself: are you really supposed to be subscribed to more than 100 queues/topics? If not, you may have a leak. Just as you wouldn't fix a memory leak by increasing memory, you shouldn't fix this leak by increasing the max flow. Are you forgetting to close your subscriptions? Are you using temporary queues? Despite their name, temporary queues last for the life of the client session unless you close them.

But if you really are supposed to be subscribed to so many endpoints, you may increase the max ingress and/or max egress. This can be done in SolAdmin by editing the Client Profile and selecting the Advanced Properties tab, or in solacectl by setting max-ingress or max-egress under configure/client-profile/message-spool (as explained here). (There is also max setting per message spool, but you are unlikely to have violated that.)