Online ad perhaps lacking nothing to be inviting (6)
I believe the answer is:
entice
'be inviting' is the definition.
(to entice is to be attractive or inviting)
'online ad perhaps lacking nothing' is the wordplay.
'online' becomes 'e' (abbreviation for electronic, e.g. in ecommerce).
'ad perhaps' becomes 'notice' (a notice is a type of advert).
'lacking' indicates named letters should be taken away.
'nothing' becomes 'O' (looks like zero - 0).
'notice' with 'o' taken away is 'ntice'.
'e'+'ntice'='ENTICE'
'to' is the link.
(Other definitions for entice that I've seen before include "Tempt, lure with nice offer" , "draw" , "Tempt with promises of reward" , "Attract with offers" , "alluring" .)