Wayland is built up of multiple orthogonal protocols that each app negotiates access to with the server. Any given app will probably use multiple of these, for output, input, etc.

Not knowing exactly what Text Expander is, I'm guessing it would probably need access to a specific protocol for controlling accessibility features. The Wayland server would need to be configured to allow this app access to that protocol somehow, for example by way of a server-initiated popup window that asks you to allow or deny this access.

Does that explain it?