Is it permissible to accept friend requests from girls on Messenger for an Islamic service, knowing that some of them post indecent pictures or seek to socialize?

The basic principle is that there is no harm in adding girls to benefit from Islamic services, as a man inviting a woman or vice versa is permissible if it adheres to Sharia guidelines and no fitna (strife/temptation) is feared. Nevertheless, it is advisable to avoid adding girls, especially since some of them post inappropriate pictures or seek to socialize, which could be an entryway for Satan and lead to fitna, as Allah Almighty says: "O Children of Adam! Let not Satan tempt you as he removed your parents from Paradise, stripping them of their garments to show them their private parts. Indeed, he and his tribe see you from where you do not see them. Indeed, We have made the devils allies to those who do not believe." (Al-A'raf: 27). Inviting to Allah is one of the greatest acts of nearness, as Allah Almighty says: "And who is better in speech than one who invites to Allah and does righteousness and says, 'Indeed, I am of the Muslims.'" (Fussilat: 33).