I followed the implementation of: https://github.com/fortinet/azure-templates/blob/main/FortiGate/Active-Passive-ELB-ILB/doc/config-outbound-nat-considerations.md
However, as soon as the IP-Pool is configured on the primary fortigate, it's synced to the failover system. As a consequence, it is not possible to create an IP-Pool with the same name but a different ip on the failover system. The failover is therefore effectively not working.