Just to confirm your setup:
- I see you are running indihub-agent on stellarmate from command line
- you use INDI Web Manager and have it running on the same stellarmate
indihub-agent has special parameter "indi-server-manager" where you put host and port of INDI Web Manager. The default value for this parameter is "raspberrypi.local:8624" - that's why it is trying to connect there but looks like it is not the right host.
Can you try:
/home/stellarmate/Public/indihub-agnt-raspberrypi/indihub-agent -indi-profile=NMCosmos -indi-server-manager=localhost:8624
Please note: the default mode of the agent is "solo" (image contribution) which can be changed via command parameter to open access for sharing equipment, you can find more info about modes here github.com/indihub-space/agent#indihub-agent-modes