Hi Ritesh,
Could you please confirm that you are trying to fetch the data for all accounts directly under a MCC account? If this is the case, then please check this sample java
code to download the reports. If not, then you could pass the client customer id during the run-time instead of defining it in the properties file. To understand how to do that, please check
this line in the above sample. Please note that, in the second case, the user authenticating the API call should be same for all the accounts.
Thanks,
Milind, AdWords API Team.