I don't know the legal text, but improving interop specifically between messaging services seems to be a goal of the DMA, according to the EU parliament [1]:

> Interoperability between messaging platforms will improve - users of small or big platforms will be able to exchange messages, send files or make video calls across messaging apps.

Lock-in mechanisms like the above would at least run counter to that goal.

I also think that enforcing device restrictions on a messaging service is more problematic than on some random API: Messengers are subject to the network effect and usually you can't freely choose which messenger you want to use - it depends on which one the people you want to talk with are on.

In an extreme case, some person or business could choose to exclusively communicate using iMessage. Then you'd have to buy an iPhone just to be able to reach them. This seems like exactly the kind of interop problem the EU is concerned about.

[1] https://www.europarl.europa.eu/news/en/headlines/society/202...