You are allowed to cancel a permit unless it falls under the falling scenario:

1. It has been utilised for cargo clearance;

2. It has expired for more than a calendar day;

3. It is an In-Payment permit with duty or tax amount being paid;

4. It is declared with a Certificate of Origin (for export permits); or

5. It has been requested by the Manifest Compliance Unit of Singapore Customs for audit purposes.

You may refer to Customs website for more information on permit cancellation for import, export and transhipment permits.