Cognitive Services Facial API Error while Creating Persongroup

I am creating Login using Face API, calling Create PersonGroup Face API for signup using name, password and photo, while calling the API its throwing fallowing error.

{Microsoft.Rest.ValidationException: 'personGroupId' does not match expected pattern '^[a-z0-9-_]+$'. at Microsoft.Azure.CognitiveServices.Vision.Face.PersonGroupOperations+d__5.MoveNext () [0x000a9] in <8de5e6fac04940fc8acf7fec01…}

It seems like pattern error for group ID, I have tried creating different patters but not woking.
So could you suggest the exact pattern for groupId to create the person group?

Thank you,