S2S API `viewer_purchases` errors

The documentation for this API suggests the following (from this page -- https://developer.oculus.com/reference/platform/v34/o_v_r_requests_i_a_p_8h😞

$ curl -G -d "access_token=$USER_ACCESSTOKEN"  -d "fields=id,item{sku}" https://graph.oculus.com/$APPID/viewer_purchases

I have used the GetAccessToken() call (from Unity) to get what looks like a valid User Access Token. I then use that value and a valid $APPID, and get the following error:

"{"error":{"message":"Unsupported post request. Object with ID '$APPID' does not exist, cannot be loaded due to missing permissions, or does not support this operation","type":"OCApiException","code":100,"error_subcode":33,"fbtrace_id":"An4VQxosLHb9uiWeDYZO5ef"}}"",

The $APPID does exist, and i have been able to use other S2S API calls using it. What is the correct way to call the "viewer_purchases" method?