Hi Martin,
Thanks for reaching out. With regard to your concern about getting "Payment Account Id" of one ad account,
- If you are referring to the AdWords API, you can use BudgetOrderservice with billingAccountID field.
- If you are referring to the GoogleAds API, you can use BillingSetup.PaymentsAccountInfo service with payments_account_id field. Please refer to this guide and you may refer to this code for getting billing setup information.
Let me know if you have any questions.
Thanks,
Nirmita Patel Google Ads team

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