Adding the tag to your favourites doesn't actually create the tag, so it doesn't matter whether you have enough reputation or not. It just adds that tag name to a list in your profile. If a tag is subsequently created with that name, the tag will be in your favourites; until then, it has no effect.
If there's an error here, it's only that the behaviour is a little confusing.
BTW, there's not much point adding a new tag if there's only one question it relates to. Tags with one or zero questions are automatically removed after some time.
We also wouldn't normally add a device tag to this particular question, because it doesn't appear to be specific to this model: the same problem could just as easily arise with a different device.