Be careful how you book MGM hotels in Vegas; My mistake cost me a valuable Hyatt perk

What could go wrong with a seven-hour overnight in Las Vegas?

For some people, it's a string of bad luck in the casino. For others, maybe it's one too many drinks. For me — a full-time traveler — it's missing out on elite credit.

In advance of an early morning preview of the newly expanded Amex Centurion Lounge in Las Vegas, I spent a very short night at the Delano. I checked in late at night and left around 4 a.m.

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Despite the short stay, I maximized all my perks by booking through the American Express Fine Hotels and Resorts program (FHR). As a cardholder of The Platinum Card® from American Express, I had access to the FHR suite of benefits, which included a ton of valuable amenities, including early check-in, guaranteed 4 p.m. checkout, an up to $100 food and beverage credit, free breakfast and more.

In fact, the $100 dining credit nearly offset the entire $109 stay (minus the resort fee, of course). I even prepaid through the Amex Travel portal to earn 5x Membership Rewards, worth $11 according to TPG's valuations.

Almost as big of a win as doubling down on an 11 and pulling a face card.

Since I was staying at the Delano, which is an MGM resort and a member of the M Life Rewards program, I asked to add my World of Hyatt membership number at check-in. This way, I could earn elite night credit and Hyatt points towards requalifying for Globalist status. (Hyatt and M Life have a partnership that allows members to earn points and match status between programs.)

This would be on top of the FHR perks I'd receive by booking through Amex, representing a fantastic double-dipping opportunity.

Related: Complete guide to the Amex Fine Hotels and Resorts program

Well, fast forward two weeks since checkout, and the elite night credit hadn't posted to my World of Hyatt account. I filled out a missing stay request, and much to my surprise, my request was denied.

"The rate you paid was an Ineligible Rate and therefore does not count toward earning Tier-Qualifying Night credits or points," read the email I received a few weeks later.

Based on reader reports and anecdotal evidence from the TPG team, I thought I'd been short-changed. In the past, I've received World of Hyatt elite credit for FHR rates at Hyatt.

So, I turned to a World of Hyatt spokesperson to find out what happened.

Unfortunately, the spokesperson confirmed that there's an interesting nuance to the M Life partnership. For a night at an M Life property to be eligible to earn World of Hyatt credit, it must be booked directly through either MGM, M Life or Hyatt. Third-party rates, including those booked through Amex, do not qualify.

As a result, my Fine Hotels and Resorts booking at the Delano was indeed an ineligible rate, and I wouldn't receive any elite credit or points.

Note that this just applies to the MGM properties in Las Vegas, not any Hyatt-branded hotels.

If I'd booked a Hyatt property through FHR, like I've done before at the Park Hyatt in Paris and others, then I would've earned World of Hyatt credit, according to the spokesperson.

Though I didn't earn any World of Hyatt credit for my night at the Delano, the FHR benefits far outweighed the elite credit I forfeited.

Now, I'll start packing for a night in a Hyatt property elsewhere to make up for the one that I missed in Las Vegas.