EDIT: After examining the screenshot closely, I see it does show a message, but uses a white font over a light gray screen. Please see if the color of the text can be changed to a darker one. Maybe it has to do with my theme in general (I did not customize my themes, so it uses whatever Google set it to and all my other apps that show toasts work fine).
Just downloaded the app on Pixel 6 Pro and tried adding my IAM programmatic ID and secret, but I was being shown what I thought was an empty toast message while the values were not being accepted.
Here's a screenshot.
