Can a tag start music on a speaker?
Yes. The tag holds an address or an identifier, the phone reads it and opens the music, and the sound then travels to the speaker by whatever connection the phone already had. The speaker never sees the tag and does not need to support NFC at all.
Where the tag sits in the chain
Three links, and the tag is only the first. The tag is read, the phone opens a music application at something, the application sends audio wherever it was already sending it.
That structure explains every failure you will meet. A tap that does nothing is nearly always the second link, and rewriting the tag will not touch it.
It also explains why the same tag behaves differently on two phones. The tag is identical; the application and its account are not.
The speaker is not involved
A speaker connected over Bluetooth or over the network receives a stream. It has no idea a tag exists and no way of finding out.
So the specification of the speaker is irrelevant to whether this works, which is welcome news for anyone about to buy one for the purpose.
Choosing which speaker plays is a matter for the music application, not for the tag, and an automation can usually make that choice as one of its steps.
The one case that is reversed
Some speakers carry a tag of their own, placed on the casing, holding what a phone needs in order to open a Bluetooth connection to them.
That is the opposite arrangement: the speaker holds the tag and the phone reads it, which shortens pairing to a tap.
It is worth recognising because people conflate the two and conclude their speaker must support NFC before any of this can work. It does not.
Building one that lasts
Write the address of something stable, such as an album or a playlist you maintain, rather than a link that a service generated for one occasion.
Put the tag where the phone is already going to be. A tag by the kettle or on the bedside table is tapped; a tag on the speaker itself means walking to the speaker, which defeats it.
Take NFC Tools. On iOS it requires an iPhone 7 or later running iOS 15.6 or later, and the app must be launched manually. Background reading is available from the iPhone XS and XR onwards.
And expect the application, not the tag, to be what eventually breaks it.
Frequently asked questions
Does my speaker need to support NFC?
No. The phone does all the reading and the speaker only receives audio by its usual connection.
Why does my music tag work for me and not my partner?
The tag is the same for both. The music application and the account behind it are not, and that is the link that fails.
Some speakers have an NFC logo on them. What is that?
A tag on the speaker holding what a phone needs to open a Bluetooth connection. That is the reverse arrangement, for pairing.
Where should the tag go?
Where the phone already is, not on the speaker. A tag that requires walking somewhere stops being used.