Is it permissible for a husband and wife to agree upon khulʿ without there being any problems, in exchange for a sum of money?

Khul' (divorce at the instance of the wife) is Islamically permissible whether there is discord or concord. Qadi Abu Bakr Ibn al-Arabi explained that the verse: "And if you [the judges] fear that they [the spouses] will not maintain the limits of Allah, then there is no blame upon them for what she gives up to free herself" (Quran 2:229) mentioned discord because it is the prevailing circumstance, but it is not a condition for khul'. This is further supported by the Almighty's saying: "But if they [the wives] give up to you anything of it [the dowry] themselves, then take it with pleasure and ease" (Quran 4:4). So, if the wife gives her money willingly, it is permissible to take it.