English to Russian Other Law: Contract(s) contracts

Расскажите, пожалуйста, что означает выражение party at fault.

Контекст:

Reduced payments as a result of the breach of contractual obligations of one party shall lead to a corresponding reduction in the payment for the party at fault. In the event that a non-payment by the end customer is caused by a breach of contractual obligations of one of the parties, the party at fault must reimburse the other party for any loss incurred as a damage thereof.