Is it permissible to supplicate with: "O Allah, forgive me, and have mercy on me, and gladden me upon meeting You. O Allah, forgive me and my parents and all of the Muslim Ummah. O Allah, have mercy on me and my parents and all of the Muslim Ummah. O Allah, gladden me and gladden my parents and all of the Muslim Ummah upon meeting You. O Allah, Amen"?

If the questioner meant by saying: "Allahumma, O forgive me" (اللهم يا اغفر لي) "Allahumma, forgive me" (اللهم اغفر لي), and the mistake was a typographical error, then there is no harm in supplicating with this phrasing. It is permissible for a Muslim to supplicate for whatever good he desires in this world and the Hereafter, using any phrasing, as long as he does not supplicate for a sin or for the severance of kinship ties, while preferring the reported supplications.