What are the legal grounds for obligating a party to pay outstanding contractual amounts and compensation for litigation expenses?

The obligation to pay outstanding contractual amounts is based on the party's acknowledgment of the transaction, or the existence of explicit correspondence confirming the indebtedness and the obligation to pay. As for compensation for litigation expenses, it can be awarded if the other party's undue delay or compelling the rightful party led to them incurring legal expenses, based on the Sharia maxim (al-ḍarar yuzāl - harm is to be removed) and the saying of Sheikh al-Islam Ibn Taymiyyah that what the rightful party spent due to the oppressor's procrastination shall be borne by the unjust wrongdoer. The compensation is usually assessed as a percentage of the value of the established right.