endpoint:80/sub is not recognized in grpcurl

Hi, I have a service endpoint as ```endpoint:80/subgrpc``` when I pass in whole grpcurl as this:
```
grpcurl -d '{body}' -H 'authorization: Bearer jwtKey' -plaintext endpoint:80/subgrpc service/serviceName
```
return log as:
```
Failed to dial target host "endpoint:80/subgrpc": dial tcp: lookup tcp/80/serviceName: unknown port
```
Did I wrongly pass anything into the command ?