Hi Phongthorn,
Thanks for reaching out. If you request on a customerId which does not contain any campaigns you would get an empty campaign list. You could use theManagedCustomerService to get all the accounts under the MCC manager account. Then with a specific clientCustomerId in the request header you would be able to query a report on this specific customer account.
Thanks and regards,
Xiaoming, Google Ads API Team
Hi Phongthorn,
You could use the CAMPAIGN_PERFORMANCE_REPORT to retrieve all the campaign data on the campaign level in the specified customer account. Please let me know if you have any further concerns.
Thanks and regards,
Xiaoming, Google Ads API Team