When I last tested it with Wallpanel in August 2020, the intent URL format was not supported in WallPanel.
I looked through the GitHub repo for Wallpanel and it looks like just recently they’ve added some level of support for intent URLs. Here’s the relevant issue from the WallPanel repo. Make sure you’ve updated to at least WallPanel 0.9.4.3 or newer.
That being said, I played with it a bit and it seems to be a bit flaky compared to Fully Kiosk. Several of my existing intent URLs worked fine, but some didn’t.