Why does the code with the Vkontakte API not work?

Question

In contact with

Created a page with text, uploaded it to hosting.
Vkontakte in the field "Address IFrame:" indicated the path to the page on the hosting: dobraya.hol.es/habr-vk-api/index.php
Of course, nothing is displayed in the application window. Here is the page on the hosting dobraya.hol.es/habr-vk-api
Is there a step-by-step instruction on how to do this correctly?
Initially, I wanted to do the following: locally (MAMP) experiment with Vkontakte methods and look at the result in the social network itself in the application window.

Answer 1

It was necessary to configure access via HTTPS in MAMP:
1) When MAMP is enabled, on the Hosts tab, by pressing the plus, we add a new virtual host, while in the Server name field we write any name, for example, www.tests.dev
2) Document root - select a directory, I created an https folder at the same level as htdocs.
3) SSL tab - click Create self-signed... - this creates a certificate, save it in the MAMP folder.
4) In the https folder, put some project for the test. (by the way, if you click on the arrow to the right of the Server name field, you will be taken to the The virtual host was set up successfully page.)
5) Restart MAMP, go to
https://www.tests.dev:8890/your_project_name...
Browser warns about something, but I click "I accept all risks" - the site is available.
We go to the VK application settings and in the IFrame Address field we write:
https://www.tests.dev:8890/name_of_your_project...