I am a US permanent resident (green card holder) and I am planning to visit Belgium. In the Schengen visa file, an itinerary proof is required. Within this doc there are the accommodation doc, which I have, and the flight ticket.
How can I purchase a flight ticket if I'm not sure yet that I will be approved (get the visa). I am confused. Please help me, my time is running out.
What constitutes "proof" is unclear, as you can see by reading the Travel.SE questions here and here. Ultimately, it will be up to the Belgian embassy or consulate or whatever visa-assessing private authority is used by the embassy or consulate.
It is sometimes possible to obtain an airline flight confirmation (not a fake or made-up ticket) without payment. Evidence-wise this is not as convincing as buying an actual paid ticket, but as seen from the other questions, might be acceptable to the embassy or consulate or visa authority. Whether you try this option will depend upon your tolerance for risk and uncertainty.
The most convincing evidence, as @Nean Der Thal notes in Comments, is to buy a refundable ticket. Refundable tickets are more expensive than non-refundable tickets. However, if the visa is not issued, you can return the unused ticket to the airline and your purchase money should be refunded to you. As in all matters related to airline tickets, you should deal directly with the airline itself, and not use an online travel agent or intermediary.
