In Zapier, go to Home > Apps

Select + Add connection.

Search for and select Marketing.

Enter your API username and API password.
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To access your API credentials in Marketing, expand the User menu and go to Settings > Access > API users. You must be the account owner or a user with the Can manage account permission enabled to view this area.

If you don’t yet have an API user, check out the article Create an API user.
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Select Yes, Continue to Marketing.

Select Test to make sure the username and password are correct.