A PAY. API token is a unique hash (collection of letters and numbers) that is required for authentication to use a PAY. API. In other words: with API tokens you tell us who you are.
By default, each merchant has one API token available, which can be found via the tab ''Merchant'' -> ''Company data''. You can create multiple tokens (for free) via the package options. You can set rights per token. You can for example create a token that only has access to financial data.