Registering a S3 repository to opensearch domain

I am trying to register a repository to take a manual backup in opensearch. Right now I am achieving this trough python script. To avoid using script, I am trying to send a api PUT request through postman but getting a error telling anonymous user not authorized to pass role. If I pass a IAM user credentials in postman as aws signature, I am getting "The request signature we calculated does not match the signature you provided".