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 below error can be found in the channel's logs and in the default traces:

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 HTTP traces collected as per SAP Note: 1514898 - Troubleshooting SAP Process Orchestration / Integration, the below response can be found:

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

SAP NetWeaver 7.5

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