Form created by Online Form Builder wil not load


I’am evaluating a trial version of DHTMLX (PC vs. 5.0.1).
I created a form in DHTMLX Form Builder and saved this as JSON-file.
Used this in the statement:

var form_1 = tab_1.attachForm();

It will not show up with testing.
Please advise me what’s wrong.

see attached zipped-file.
my_Demo.7z (899 KB)