Buying Dawntrail for 2nd service account on same SE account (Steam)

When I add Dawntrail expansion to my shopping cart it says,
"If purchasing for yourself, you will not receive an extra copy of: FINAL FANTASY XIV: Dawntrail"

So, how can I upgrade a 2nd service account that is on the same Square Enix account? Has anyone done this? Can I buy it as a gift to another Steam account and then use the keys on my service account, or will they be locked to that Steam account?

Even when I go from the Mog Station on that service account and select "Additional Expansions" it just brings me to the Steam page or gives me the option to enter a key.

Dont buy anything outside Steam, if the account is a linked steam account. Versions from the mogry station are incompatible with the steam versions.
You need to buy dawntrail via Steam for ayour second steam account. Login via the correct steam account for sure.

Yeah so I think I figured it out. I made a 2nd steam account, tried both buying on and gifting to that account but it tells that it doesn't own the base game to be able to buy/receive. So even though that 2nd account recognizes that I have the base game installed under my main account, I still would need to buy the complete XIV edition to upgrade. It's crazy because all I needed to do to unlock the base game from the free trial on the 2nd service account was start paying for the subscription. During this research I found that the XIV free trial is on Steam as a completely different install/game, but I don't think that works (I kinda gave up at that point, or just forgot).

What the message means basically is that, if you purchase the DLC again, you will NOT receive a second CD key, you will get the same CD key again that you received the first time you purchased the DLC.

This is true for the Starter Edition, Complete Edition and the separate DLC (Dawntrail) on Steam.

The only way to obtain a second CD key of the Starter Edition with all DLC included on the same Steam account is to purchase the Complete Edition, but ONLY if you have never purchased the Complete Edition before (handy if you have only ever purchased the Starter Edition and/or separate DLC), it will give the same warning, but you can ignore it as you will get a new CD key in your keys list titled "Complete Edition", (if you already have this titled key, don't buy it again).

I'm unsure if it is possible to have two Steam version Square Enix "service accounts" linked to a single Steam ID, I think not, making it impossible to activate a second Steam CD key on say, "SE Service Account 2".

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