3398094 - error: com.sap.aii.af.sdk.xi.oauth.json.JSONException: A JSONObject text must begin with '{'  when fetching Rest OAuth access token

The rest adapter receiver communication channel is not able to retrieve OAuth access token.

The bellow error can be found in the channel's logs and in the XPI inspector traces example 50:

 
Error while processing Authorization request!
[EXCEPTION]
com.sap.aii.af.sdk.xi.oauth.json.JSONException: A JSONObject text must begin with '{' at 1 [character 2 line 1]

In the XPI inspector http traces you may find:

HTTP_CLIENT : xxx REPLY: 
3cd.....{"access_token":"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"}..0..

SAP NetWeaver all versions

com.sap.aii.af.sdk.xi.oauth.json.JSONException, A JSONObject text must begin with '{' at 1 [character 2 line 1], Rest Adapter, OAuth, access token, refresh token , KBA , BC-XI-CON-RST , Rest Adapter , Problem