@HelenDoan 

I didn't mentioned about creating a dummy bank account. You may open the SGD bank account at TW as a workaround. e.g with the current exchange rate, you will receive SGD 7,58 in your account when your customer paid IDR 100.000. Run the bank feeds if required.

The same process with your bill payment. You may transfer out SGD 200 from your TW account and your vendor will receive IDR 2.128.613. 

Just my 2 cents.