in reply to Why is mojolicious "routing to a callback" ?

"Routing to a callback" means calling a "sub { ... }" instead of a to('somecontroller#someaction'). If you give it a name it will print the name instead of just "a callback". (conversely, you can embed any of them with a sub{} callback instead of a name and it will say just "Routing to a callback" instead of "Routing to controller/action".

It is probably calling your $r->under() sub and failing.