Phone prefix from int-tel-input won't show in Webflow Logic

Hi all,
I am working on a client’s website with a form calling their API with Logic and the form has a phone with a prefix. I have added the phone prefix with this javascript plugin -

But even though the prefix is a normal input field, it is not appearing in the Logic flow and I can’t add it to the Body of the HTTP request, which is really strange.

Can anyone help me out with this? I am providing the read-only link below:

Thanks in advance!