MEIS Duty Scrip Accounting

When MEIS Duty Scrip received on Export is considered as income:

1. At the time of Export.
2. At the time of Receipt of Certificate
3. At the time of sale of MEIS scrip.

Scenario:

I have Exported Agricultural goods to X Co. in Dubai on 20/03/2020 and received MEIS scrip Certificate on 02/04/2020 and sold the same Certificate to A Enterprise on 05/04/2020.
Now when and i have to record this transaction in my books (what is the proper Accounting entry as per the rules)?

Thank You in Advance, your advice is valuable.