I have the following label in my alert:

I have the following notification policy:

I also have the following contact point:
Yet when I preview message routing the following happens:
WHY???

Double check if you don’t have any white characters there.
It may look the same, but I can imagine that space was somewhere copy&pasted, so they are not the same actually.
Spinning up third server to test again
Try to generate real alert. Maybe only routing preview has a bug.
Submitted a bug report. No response