API Permission Issue

Hi Team,

We have one trial account and we are using 

"POST /agreements/{agreementId}/members/participantSets/{participantSetId}/delegatedParticipantSets"

and  in the response we are getting below mention error

{ "code": "PERMISSION_DENIED", "message": "The API caller does not have the permission to execute this operation" }

Please help us in this.

Thanks