getCampaigns.java returns an empty list. might be an account problem.

[mktt.s...@gmail.com]

I encountered a problem while i was getting started to use Ads API. 

The getCampaings example is not working as i expected. 

I, my Company has an google ads MCC account, say ACCNT_A, that has several sub_accounts, 

and each of the sub-accounts  has valid campaigns. 

And i created a dev account ACCNT_B, and made a link to ACCNT_A. ( ACCNT_A sent an invitation to ACCNT_B)

Access level of ACCNT_B was shown as "Standard" in "toos" manue of ACCNT_A

I then confirmed that  ACCNT_B  could access all of ads in ACCNT_A and it sub-accounts, via Web site. 

For API use, 

I created developer token in ACCNT_B , and credentials, and executing getCampaings was working without Exceptions. 

But, it returns an empty campaign list, as below

Response

--------

Headers: Metadata(content-disposition=attachment,content-type=application/grpc,request-id=cvog8hAsxxxtSKsdfzrffGsIDpasdfxAdsaf,date=Wed, 20 Mar 2019 11:26:20 GMT,alt-svc=quic=":443"; ma=2592000; v="46,44,43,39")

Body: field_mask {

  paths: "campaign.id"

  paths: "campaign.name"

}

Status: Status{code=OK, description=null, cause=null}.

I tried ACCNT_A and ACCNT_B for the CUSTOMER_ID property, returns the same, empty list without exceptions. 

when i tried with sub_accounts of ACCNT_A, in which campaigns are actually registered, permission error occurs as below. 

 Error 0: error_code {

  authorization_error: USER_PERMISSION_DENIED

}

So, please tell me what was the problem?

Do i need to get permissions to each of sub_accounts?

or, was there anything wrong my account usage?