Getting Unable to determine service/operation name to be authorized - AccessDeniedException Error on CreateParticipantConnection

Question

I am trying to test the Amazon Connect Chat API in POSTMAN,

1. The first part StartChatContact tested/executed and i have got the ParticipantTokenback in response with ContactId & ParticipantId by using PUT: https://connect.us-east-1.amazonaws.com/contact/chat
2. But i am unable to run the POST: https://connect.us-east-1.amazonaws.com/participant/connection. here is the Request Syntax AWS has given:

POST /participant/connection HTTP/1.1

X-Amz-Bearer: ParticipantToken
Content-type: application/json

{
   "ConnectParticipant": boolean,
   "Type": [ "string" ]
}

i have tried the ParticipantToken as header parameter with name mentioned in documentation (X-Amz-Bearer: ParticipantToken) as well as used in Authorization as Type API Key & AWS Signature. But can't get rid of this error. In response Headers i got x-amzn-ErrorType: AccessDeniedException and in body

{
        "message": "Unable to determine service/operation name to be authorized"
    }

How to remove this error? any solution please.