Adding to what @Brucanna said, a purchase invoice records an obligation to pay a Supplier. It adds to Accounts payable. But you do not owe anything to a Supplier. As a company, you owe yourself, because your private funds were used to buy something for the company. If you have read the Guide, you know that this obligation can be handled by (1) actual reimbursement or by (2) clearing it to a capital account or owner’s equity.