Internal Standard Load balancer with syncMode

[pattisanta]

I am having deploying a standard regional internal balancer with syncMode set to Automatic.
I have tried to deploy an empty back end pool. Then deploy the backendAddressPools I get an error Sync mode property on pool cannot be updated. It is set to Automatic on the existing pool.
I have tried to deploy backend and backendAddressPools and I get an error "SyncModePropertyCannotBetSetWithLoadBalancerBackendAddressesPresent","message":"Sync mode property of load balancer backend address pool cannot be set with backend addresses present in the pool.

Thanks,
Patti