I am trying to replace a short-text input field with my custom input field, like in arrayTextAdapt. But my answer does not get saved in the survey response.

From arrayTextAdapt, it seems I only need to use the same id (e.g., answer123456X3X23) in my custom input field as in the existing input field. But this does seem to be enough. Please help.

Same name it's the most important

name => sent to PHP
id => used by javascript (and label)

Aha!
After setting the name attribute to "123456X3X23" it works now.
Thank you so much!