Yes, you can run ads for your client through their Business Manager and use their payment method, even if you don’t have your own Business Manager—as long as you’ve been granted the right permissions.
1) Access to Their Ad Account
You must have at least Advertiser access on their Ad Account within their Business Manager.
2) Use Their Payment Method
The ad spend will be billed to whatever payment method is attached to their Ad Account (not yours).
You don’t need to add your own payment details.
3) Campaign Setup
You can create and manage campaigns using their Ad Account, and Meta will charge their credit card accordingly.
Key Notes:
You won’t be able to share or transfer campaigns from your personal Ads Manager to their Ad Account.
If you’re running ads regularly for clients, consider creating your own Business Manager for better control, transparency, and access management.