Thought i should write a small post about setting up a Site to Site VPN between Azure Resource Manager and a Fortigate Firewall on 5.4.
Important thing to notice here. Use Route Based VPN Type on the Azure Virtual Network Gateway for this.
I used this guide to setup our Azure IPsec tunnel from Microsoft. I recommend using there guides when it comes to azure setup. Combine these with other relevant guides. Make sure they have been recently.