I tried to look at similar questions but they are of no use for me.
I have a class:
data class TextMessage(val text: String,
override
The problem in your code is that you are using a field named isText. In Cloud Firestore the coresponding getter is getText() and NOT getIsText() as expected.
If you try to change the name of the field in, let's say, izText instead of isText and to have the corresponding getter like getIzText(), your code will work perfectly fine. Firestore removes the is prefix from the getter, that's why you have that conflict. For more informations, you can also take a look at this video.
If you decide to change that field name, don't forget to remove the old data and add fresh one.