Zeplin normally sends invoices to the email associated with your account. You can also set a different billing email for receiving copies of your invoices.
Setting a billing email on the Team, Organization, and Enterprise plans
You can set a billing email by clicking the settings button at the top of your Workspace Members page and going to the workspace Billing tab.
Only members with an Admin role or higher can access the "Settings" button and billing information.
☝️ If you're on the deprecated Starter or Growing Business plans, you can set a billing email from the billing tab in your profile.