What should a Muslim do who intended to pay Zakat al-Fitr in Ramadan while performing Umrah, but at the time did not possess enough money to pay the Zakat and cover the expenses of his and his family's return to their country, knowing that he owns money in his home country? Is it permissible to pay Zakat after its designated time, and what is the expiation for that?

Zakat al-Fitr must be given in the place where it became obligatory. The time it becomes obligatory begins with breaking the fast on the last day of Ramadan, and it is permissible to give it before then. It is obligatory upon every Muslim for themselves and for those whose maintenance is their responsibility, provided their wealth exceeds their and their family's sustenance for the day and night of Eid. If one does not have wealth in the country where it became obligatory, they may appoint someone to give it out on their behalf from their home country. If they fail to do so due to an excuse, they should give it later, and there is no sin upon them.