Determining the legitimacy of an Apple text message

Apple rarely send text messages, so you're right to be wary.

Scammers are crazy and creative, and it's easy to get fooled. Just just know that Apple never sent text messages telling you your iCloud subscription is expired/expiring, or that your iCloud storage is full, or that there was a problem with your payment card, or anything like that.

There should also never be a link to click directly to respond to the text.

The only text you might receive from Apple is for two-factor authentication, if you're trying to log into your iCloud account on a new device, but even then they're moving (have moved?) away from text messages to direct popups on your iOS device, so that a) shouldn't be common, and b) should be in response to an action you took, so you should be expecting it.

That's easy. It isn't.

Whatever you got, it is almost certainly a scam.