How can one get rid of inner weakness, the inability to resist desires, and excessive spending resulting from the soul's insistence on buying everything it fancies, which leads to the loss of inner peace and contentment?

We ask Allah to grant you success, guidance, reform of the heart, and protection from the evil of the self. The imams have dedicated numerous works to discussing the self and its afflictions, including Adab al-Nufus (Etiquettes of the Souls) by al-Muhasibi, and al-Akhlaq wal-Siyar fi Mudawat al-Nufus (Ethics and Conduct in Healing the Souls) by Ibn Hazm. Moreover, books of Riqā'iq (heart-softening literature) generally address this topic. You can also refer to fatwas: 64719, 64574, and 68168 for reforming and purifying the self.