HTML number inputs will throw a native validation error when submitting a float:
https://formkit.link/079bded4a052e50851e47c85d7b26adb
Settingstep to any avoids that validation error:
https://formkit.link/53394a3b41d0c5cf216602e9d46000b6
This should be mentioned explicitly in the documentation for the type="number" FormKit input.