This should work without issue.
Something is likely blocking the traffic somewhere, so here are some places to start:
1) Make sure NSGs in both the spoke VNET & firewall subnet allow traffic between the VNETs.
2) Make sure your Palo Alto firewall allows traffic from the spoke VNET. Also, test your VNET to VNET communication and see if there are any blockers. Also, does your hub VNET have any issues with internet access?