Yes, you can absolutely purchase travel insurance booking your flight. In fact, most insurers allow you to buy a policy up until the day before you depart.
While you can buy insurance late, acting quickly—ideally within of your first trip payment—unlocks "time-sensitive" benefits that disappear as your departure date approaches. can i buy travel insurance after i book my flight
Can I Buy Travel Insurance After Booking? | Allianz Partners Yes, you can absolutely purchase travel insurance booking