What are the obstacles or sins that prevent the answering of prayers, and can one repent from them?

Ibn al-Qayyim clarified that the impediments to the acceptance of supplication include sins in their entirety, especially heedlessness and consuming unlawful earnings, because they weaken the heart and diminish its receptiveness to Allah. Supplication is an effective remedy, but the heart's heedlessness of Allah and consuming unlawful earnings nullify its power. A supplication from a heedless, distracted heart will not be answered, and Allah accepts only what is good. The supplication of one who consumes unlawful earnings will not be answered. Sincere repentance from these sins removes the impediments and becomes a reason for the acceptance of supplication.