Azure Function App SignalRTrigger not invoked - StatusCode 404 error

Question

Setup

Azure Function App using Isolated worker process and implementing SignalR with a Class-based model and Strongly typed Hub. Resources are manually provisioned on Azure and connected using connection strings stored in a Key Vault. RBAC is configured using system assigned managed identities.

Problem

The application works as expected locally with the SignalR emulator, where negotiation, connection, and invocation of SignalR triggers occur successfully. However, when deployed on Azure, the application can negotiate and connect, but invocation of SignalR triggers fails. The SignalR Live Trace Tool shows a HttpHandlerUnexpectedResponse with a StatusCode: 404.

Theory

There is a suspicion that the issue may relate to SignalR Upstream Settings. Attempts have been made to use the signalr_extension app key from both the Key Vault and directly in the URL. Additionally, CORS settings have been adjusted on both the Function App and the SignalR service.

// Configure SignalR
builder.Services.AddServerlessHub