Zakat fitrah must be paid in the country where we reside during the period when zakat fitrah is compulsory, that is just before end of Ramadan and before the Eid prayer. Thus, if one is in Singapore during that time, one is obliged to pay zakat fitrah in Singapore. If one is in another country, one can pay zakat fitrah at that country. But to pay zakat fitrah in another country when one is residing in different country, it is not allowed.