Every Schengen consulate asks for evidence of your intended travel. In practice that means a round-trip itinerary with your name, dates and flight numbers on it — not necessarily a paid ticket.
Most consulates explicitly advise applicants not to purchase tickets before a decision is made. A held reservation satisfies the checklist while keeping your money safe if the application is refused.
Make sure the dates on the reservation match the dates on your application form and your cover letter. Mismatched dates are one of the most common reasons an application is returned as incomplete.
Submit the reservation as a clear PDF. Keep the confirmation reference visible so the consulate can verify it with the airline if they choose to.
Build a verifiable reservation