If you earn foreign income, you may be subject to tax in that foreign
country. However, you may claim tax benefits if there is a DTA between
Singapore and the foreign country (also known as treaty country).
The DTA is an agreement signed between Singapore and the treaty country that
serves to relieve double taxation of income earned in one country by a resident
of the other country. The main objective of a DTA is to provide certainty
regarding when and how tax is to be imposed in the treaty country where the
income-producing activity is conducted or payment is made. Under the DTAs, the
treaty countries may provide tax breaks (e.g. tax credit or exemption) to tax
residents of Singapore on income derived from their jurisdictions.
Non-residents do not enjoy these benefits.
To enjoy the tax benefits, you need to submit the COR to the foreign tax
authority to prove that you are a Singapore tax resident.