Hi @prasantc , I understand that you want to use existing Azure Firewall for your vWAN Hub.
You can't use existing Azure Firewalls that are outside of your vWAN Hub, you need to create a Secured Virtual Hub (vWAN Hub with Azure Firewalls inside it). How? Using Firewall Manager in the Azure portal, you can either create a new secured virtual hub, or convert an existing virtual hub that you previously created using Azure Virtual WAN.
Please accept an answer if correct. Original posters help the community find answers faster by identifying the correct answer. Here is how.