If you book a second subsidised flat (Executive Condominium),  previously you had bought & sold the first subsidised flat (BTO/ Resale HDB with grant), currently holding a resale HDB flat without any grant.

 

If you submit an application to sell your first subsidised flat and subsequently book a second subsidised flat (Executive Condo)

•  The resale levy has to be paid in cash to the relevant authority before you can take possession of your second subsidised flat