The bill for Elon Musk’s purchase of Twitter is coming due, with the billionaire facing unpalatable options on the company’s enormous debt pile, ranging from bankruptcy proceedings to another costly sale of Tesla shares.

Three people close to the entrepreneur’s buyout of Twitter said the first installment of interest payments related to $13 billion of debt he used to fund the takeover could be due as soon as the end of January. That debt means the company must pay about $1.5 billion in annual interest payments.

The Tesla and SpaceX chief financed his $44 billion deal to take Twitter private in October by securing the huge debt from a syndicate of banks led by Morgan Stanley, Bank of America, Barclays and Mitsubishi. The $13 billion debt is held by Twitter at a corporate level, with no personal guarantee by Musk.