Advisable to include endorsement (4)
I believe the answer is:
visa
'endorsement' is the definition.
(visa is a kind of endorsement)
'advisable to include' is the wordplay.
'to include' says the answer is hidden in the clue.
'VISA' is hidden within 'advisable'.
(Other definitions for visa that I've seen before include "ID" , "Stamp affixed to passport as permission to enter country" , "Authorisation to enter a country" , "giving you access to capital?" , "Mark on passport" .)