I'm the farthest thing from a Marriott bootlicker, but I don't think you were really due the $100. When you mobile check-in, the app defaults to points with a message telling you to ask front desk if you want to change it. That reverses the onus onto you to ask, rather than for them to prompt, so no compensation would be due. In terms of the lounge guarantee, I assume the property has no lounge and is not a resort, right? While non-resorts in the US are obligated to provide lounge access or, if it's closed or non-existent, choice of breakfast or points, I don't think it's reasonable to enforce the guarantee unless you've actually finished checking in. Taking a step towards the elevator falls short, IMO, because you are still down at the front desk as part of that initial check-in interaction and the conversation isn't necessarily over (just like if you took the key and ran to go use the washroom before the staff got to explain the benefits, that wouldn't entitle you to compensation just because they didn't say everything they wanted to say yet). That said, I recognize you may feel like technically it's due, based in a literal reading of the T&C, and what happened afterwards and their poor attitude may make you less willing to empathize. Generally speaking, there is typically an obligation of good faith in contractual dealings, which includes giving the other party the opportunity to perform their side of the contract. If you have knowledge that, if shared, you know would allow them to perform, and if withheld, may induce them to breach their obligations, then I would feel an obligation to share that information. I'm speaking personally and ethically, rather than legally, as obviously law varies by jurisdiction, but this is a basic principle I think is universally true in terms of dealing with others fairly and reasonably from an ethical perspective.

Besides, do we really want to operate under a literal, technical interpretation? Elites spend a lot of time in hotels, often many hotels. Many of us appreciate fast check-in experiences. And often that is part of why we choose to use the app. Hotels have a ton of info they can throw at us during check-in -- e.g., hours and location of gym, pool, spa, laundry, restaurant(s), shuttles, how to navigate the room from downstairs, policies about max people in room or noise or smoking, current special promotions -- in addition to elite-specific info. Often it goes in one ear and out the other. Staff will often skip over what they think is less relevant or important to us (sometimes it hurts when they take a look at my physique and skip over gym info ), or what they think we might already know. Sometimes they mistakenly assume based on our familiarity that we've stayed before (without checking) and just do the basics. It's not that unreasonable to expect elites to expressly ask for what they want to know. In my humble opinion, the proper purpose of the guarantees are to force hotels to honour benefits, i.e., actually deliver the good or service that is promised, not to simply waste everyone's time proactively explaining when not asked.

In addition tot he above, I'll also add that it wasn't the right time to ask for the compensation while still downstairs. If you didn't yet know whether there was a lounge, for all you knew your card was coded for lounge access and/or you could just walk into the lounge and give your room number (where ever the lounge might be, but usually indicated in the elevator if not on the ground floor). If no lounge, it seems apparent the hotel would have honoured restaurant breakfast if you had clarified "where do I get the elite member breakfast?" or even if you just ate in the restaurant and gave your room number per usual. I would only think to enforce the lounge guarantee if you were refused breakfast, were forced to pay for breakfast and they didn't take it off your bill, or if they refused a request to take the points instead. All that is to say I wouldn't have asked for the compensation, and I certainly wouldn't have pressed for it.

That said, there are bigger issues in your story about this property and Marriott more generally.

First, corporate policies and these guarantees are poorly drafted and not well understood by staff nor elites. What's the point of a guarantee if nobody knows what's guaranteed? What's the point if staff won't honour it or guests don't know when it applies? If staff aren't well enough trained to mention breakfast to elites, in what world will they know the T&C from the corporate website? Guests shouldn't be expected to memorize T&Cs to get what they are entitled to. Properties shouldn't need the stick of $100 guest compensation in order to follow corporate and brand standards. This scheme really serves no-one well.

Second, it sounds like the staff (incl. manager) are poorly trained at this property, not particularly bright, and not pleasant. It's pretty absurd to give a guest a $100 bill if you don't agree it's owed. It's even more absurd to then do your investigation and ask for it back. There's the possibility the manager felt physically intimated or threatened or tricked, or may even claim they were even if in reality they weren't but needed to provide an excuse when someone higher up questions their decision to give it to you. Maybe you didn't appreciate being banned by the property, but it sounds like it was a blessing. There are likely more systematic management issues at play.

In terms of next steps, I would ask for a letter signed by the GM apologizing for the staff's mistake and confirming you have permission to return to the property (in case you ever find yourself back there for whatever reason and the manager tries to trespass you, staff raise an accusation in the future that you threatened/harassed them or stole or got them wrongly fired or whatever, or in case Marriott corporate investigates you in the future and doesn't treat this hotel's claims against you). I probably wouldn't return in any event. I would expect the GM, learning about what happened from the process of being asked to issue a written apology, to proactively comp the night. But I wouldn't ask for anything other than just the letter.

Nothing in this comment constitutes legal advice.