error configuring static route with SD-WAN

Hi guys,

I'm configuring sd-wan with LB and when i tried to confiugre the static route i get the error attached.

i've check from the interfaces that the 2 wan aren't in use in any rules right now 

but i still get this error.

I've follow this guide: https://docs.fortinet.com/document/fortigate/6.0.0/cookbook/990932/redundant-internet-with-sd-wan

Please anyone could help me to understand this error?

Thank you very much!

Michele.