Imagine you set an award alert months ago for a flight you want to book. Your award alert finally pinged, so you searched, saw the award space and transferred rewards to book the award. But when you reach the final stage of the booking process, you get an error message because there actually isn't any available award space for your itinerary. You try again and get the same result.

Unfortunately, you've discovered what is known as phantom award space.

Phantom award space refers to award seats that appear in online searches but aren't actually bookable. This issue usually occurs when the inventory displayed by one loyalty program doesn't match what the operating carrier will actually confirm, often due to stale data or communication issues between reservation systems.

Phantom award space is one of the most frustrating aspects of booking award flights. And, unfortunately, based on TPG staffers' experiences, phantom award space isn't all that rare. So, in this guide, we'll discuss some steps you can take before transferring your rewards to avoid being deceived by phantom award space.

Why you should care about phantom award space

Phantom award space is most troubling if you're looking to transfer rewards from a transferable rewards program to an airline to book an award.

You'd likely do this because the airline you want to fly with isn't a transfer partner for the currency you're trying to redeem or because you can book through a partner airline loyalty program at a lower rate.

For example, you might transfer Citi ThankYou Rewards points to American Airlines AAdvantage to book a Japan Airlines premium cabin flight.

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But the problem arises if you transfer your rewards and can't book the flights you want. You typically can't reverse a transfer, so your rewards become stuck in that program.

Related: 6 no-annual-fee credit cards that earn transferable rewards

Consider booking with the operating carrier

The root cause of phantom award space is often stale data or a communication error between a loyalty program's booking engine and the partner airline's inventory management system. Therefore, you'll generally avoid the partner-related phantom award issues discussed in this guide when booking through the operating carrier.

So, if you can book the award through the operating carrier at a competitive rate using points or miles that you have, this is usually the most straightforward option.

However, there's often a compelling reason to book through a partner program. And just because a program offers award space for flights it operates to its own members doesn't mean it will make that space available to its partners.

Related: The same flight, half the miles: Making this award booking mistake could cost you

Do your homework on the airline

Some airlines are known for showing more phantom award space than others.

As such, it's important to familiarize yourself with the program you're trying to book through. For instance, TPG staffers have recently encountered phantom awards through several programs, including American Airlines AAdvantage, United MileagePlus, Air France-KLM Flying Blue and Air Canada Aeroplan. To this point, a message on Seats.aero recently noted Flying Blue has been experiencing increased phantom award space.

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It's equally important to research the airline you're hoping to fly. For example, TPG video producer Isabella Boccasino called Qantas to confirm premium cabin award space she was seeing through its program for a Japan Airlines flight from New York to Tokyo. During the call, the Qantas agent said the space wasn't actually available and told her phantom award space on Japan Airlines flights is a common issue for Qantas members.

Try getting to the checkout page

One of the easiest ways to check if the award space you see is real is to go through the booking process.

After all, you'll get an error message at some point during the booking process if the award space isn't available. However, this method won't work for many travelers who must transfer rewards into their account before they can book the award. That's because many programs won't let you reach the final checkout page unless you have enough rewards in your account to book the flight.

Related: The best credit cards for paying taxes and fees on award tickets

Hold your award

Some airlines let you put award tickets on hold before booking. A hold can provide additional reassurance that the program has found the award space and give you time to transfer rewards.

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However, a hold doesn't always guarantee the space is actually held for you. So, you should try to book the award as soon as possible after placing it on hold.

Cross-check award availability

One of the most important steps for verifying award space is to search for the same flight through multiple partners. If multiple partner programs independently show the same award space, that's a good sign the inventory is real. However, keep in mind that multiple partner programs may show the same phantom availability.

Award space isn't necessarily phantom if you can't find it through another partner, though. After all, airlines often provide different inventory to different partners.

Additionally, don't trust the availability you see through your favorite award search tool (such as Seats.aero or Point.me) to be real. Before transferring rewards, confirm the space directly with the loyalty program you plan to book through, rather than relying solely on an award search tool.

Call the frequent flyer program

Another useful option is to call the customer service desk for the mileage program you plan to book with and have it manually confirm whether the award space you found online exists before you transfer rewards into the program.

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However, even an agent's confirmation isn't foolproof, particularly for partner awards.

Ask to reverse your transfer

Suppose you've already transferred your rewards and determined there's no way to redeem them for your originally intended ticket. In that case, you could ask your credit card company and the mileage program to reverse the transfer.

The chances of reversing a transfer are extremely slim, so don't be surprised if this doesn't work. However, there have been rare cases in which programs have worked with transferable currency programs to reverse transfers, such as after Flying Blue canceled awards it said it priced incorrectly.

Bottom line

Phantom award space can turn an exciting award find into a frustrating problem, especially if you've transferred valuable rewards into a program.

Unfortunately, there's no foolproof way to verify partner award space before booking. But cross-checking with other programs, calling the loyalty program and placing the award on hold when possible can reduce your risk. And, most importantly, don't transfer rewards until you've done as much verification as you reasonably can. After all, transferable points are most valuable while they're still transferable.

Editorial disclaimer: Opinions expressed here are the author’s alone, not those of any bank, credit card issuer, airline or hotel chain, and have not been reviewed, approved or otherwise endorsed by any of these entities.