issue for HA fG remote

Hello everybody

We have topology in bleow:

Topology: FG-VM 112 <----- 3rd party Router -----> FG-VM 212

we want to apply HA between 2 remotes fortigate 

we use the doc https://docs.fortinet.com/document/fortigate/7.6.0/administration-guide/346301/layer-3-unicast-standalone-configuration-synchronization

We configured this correctly as per the documentation for L3 standalone unicast but it did not work

can you help us 

thanks for all