The solution to the error “Service virtual port has existed already

 I noticed once on Huawei MA5683T when I added the service port for ONT the following error:

FAILURE: SERVICE VIRTUAL PORT HAS EXISTED ALREADY

As reported by the error, the service port is already registered for this ONT.
In my case, there was simply a misprint in ONT ID, it was accidentally indicated by the wrong one, after specifying the correct service port, it was registered.

And if you need to register several service port for one ONT, then see my article – Adding an ONT with trunk port to Huawei SmartAX MA5683T