Citizens of some countries need supporting documents in order to travel to Turkey on an eVisa (visa or residence permit from Schengen area, US, UK or Ireland). You would be informed of this while applying.

These documents need to be valid (by date) when you enter Turkey. Single entry visas (used or unused) are accepted as long as their validity date covers your entry date to Turkey. 

eVisas of other countries are not accepted as a supporting document.