Typing a numeric sequence within multiple texftields

I am using character length in one field. but it takes an extra click to jump through the fields.
How can it focus the second field after 4 digits are filled?

What you have should work if you cut the code from Key Down and paste to Key Up

For usability, you’ll also want to add some logic to test that the key pressed is not a “navigational” key like Left or Right or Tab or Shift-Tab. You can combine all this in one Case.