The authorization grant type is not supported by the authorization server

[toolfolks (Stephen Warburton)]

I have followed this video GraphQL on FreePBX – Matt Brooks - YouTube

I am using postMan to connect to my API machine to machine to get a token.

http://pbx.xxxxx.com:83/admin/api/api/token
grant_type = client_credentials
client_id = myID
client_secret = mySecret

I am getting this returned.

{
    "error": "unsupported_grant_type",
    "message": "The authorization grant type is not supported by the authorization server.",
    "hint": "Check the `grant_type` parameter"
}

What am I doing wrong here please.