If you are using other platforms for trading crypto and exiting positions in SGD, the only way you have right now is thru xfers. Today, Gemini announced that it supports SGD payment.
You can now buy crypto instantly with SGD using a debit card, or if you have a Singapore bank account and phone number, you can make SGD deposits to the Gemini platform using FAST transfer. SGD trading is now available on both the mobile app and on desktop.