My question involves business law in the state of: California

Hello,

I am a supplier to several large restaurants in Los Angeles County. Recently, one of my long-time clients have gone out of business and have refused to pay their last statement prior to closing down. I am very unfamiliar with business law and I want to know if this restaurant is legally responsible for paying off any existing debts that they owe me prior to going out of business. If so, who would be responsible (the owners?) and what steps should I take? Thank you all very much for your help, it is greatly appreciated!