Every company has "capital". Even if you have a one man company, you probably stated something like "100 shares of $1 each", which means you had to take that $100 out of your own private pocket and pay it into the company.
When the company loses money and runs out of cash, they have the possibilities of (1) borrowing some money from the bank, or from a loan shark, (2) borrowing some money from the company owners, or (3) increase the share capital, for example by increasing the number of shares to 10,000 and each share holder pays his part of the $9,900. That's the case that you have here.
However, it is only a "liability" in the sense that it isn't money the company earned, it is money that the owners paid in. They have no right to get the money back; the paid-in capital is actually what the owners lose if a limited company goes bankrupt.