Is it permissible to earn money from developing or maintaining websites, such as 250 Riyals for developing or maintaining a website? And would I be sinful if I later discovered that the website owner had placed prohibitions, such as female images or music sections, after I finished maintaining the site, knowing that I had previously stipulated to him not to support these prohibitions?

It is permissible to work in the development and maintenance of websites, provided that it is not known or highly probable that these websites display forbidden content, due to the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." If forbidden content is later discovered after no negligence in searching, there is no sin, according to the Almighty's saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended."