Tesla delivered its largest-ever bond payment Friday, a move that likely used up nearly a quarter of its cash at a time when the company faces increasing scrutiny from regulators and investors, WSJ reported.

The electric car maker had issued $920 million in convertible, senior notes five years ago, a period when rapid growth and optimism around its Model S electric car drove a furious rally in Tesla shares. Reflecting that, the strike price for the notes, or the level at which the notes would be fulfilled by a conversion into Tesla stock, was $359.87 a share, or 42.5% above the level at that time.

Yet because shares traded below that level recently, Tesla TSLA, -7.84%   had to make good on its obligation using cash. That likely wiped out a substantial portion of the $3.69 billion in unrestricted cash and equivalents the company reported at the end of 2018.