Registering Microsoft as a supplier to Azure Marketplace clients

Corporations buying Azure Marketplace transactable offers in the ISV Success Program are billed by Microsoft and need to pay Microsoft either by credit card or wire transfers. To accept Microsoft bills, and pay them, those corporations need to have Microsoft previously registered as a supplier. Can anyone explain the procedure for a corporation to register Microsoft as a supplier? Is there a specific Microsoft department that buyers should contact? How have other ISV Success Program participants resolved this? Thanks!