Things to consider when adding an Ad Account to an existing Multi-Account Budget;
Be mindful of the budget target and the automation options that will more than likely need to be updated once you include spend from the new Ad Accounts(s)
Any Child Budgets that exist under the Ad Account you add will be moved under the Multi-Account Parent Budget
1. Edit the existing Multi-Account Budget by;
Clicking the name of the Budget
Selecting 'Edit Budget' from the triple-dot menu on the budget row
2. Using the Ad Account dropdown, select the Ad Account(s) you want to add.
Note: You can only add Ad Accounts that are not already part of a Multi-Account Budget
3. Click save
Automation warnings
If there are automations or a campaign selector enabled on the Multi-Account Budgets, a warning will display to ensure you check these settings before you save
