Unable to authenticate - Application Channel

I’m testing out the postman libraries shared from front.

When testing out the Sync Inbound message endpoint, no matter what I do/chnage I get the below error. 

Anyone else seen this?

{

"_error": {

"status": 401,

"title": "Unauthenticated",

"type": "resource_unavailable",

"message": "Invalid token"

}

}