To make a Failover IP work in the online.net or the OVH cloud you need to specify a gateway outside of the range of your external IP.
Something like this for example
IP :212.83.158.x
SUBNET: 255.255.255.255
GATEWAY: 62.210.89.1
But in de Gui de SYNO does not except this Gateway IP.
Windows Machines and other LINUX machines can handle this and automatically create a route to 62.210.89.1 to make this work.
But how can i get this to work on my XPENOLOGY..