Without a security certificate, the money paid for the holiday may be gone in the event of a bankruptcy of the organizer. The protection only applies to a package tour and not to the booking of individual services such as a flight or accommodation.
The travel insurance certificate can be found on the back of your travel confirmation or separately attached to the travel documents. If the tour operator is already insolvent before the start of the trip, the insurer can decide whether the trip will still be carried out or cancelled. If you demand reimbursement of the travel price, the insurers must pay immediately.