[NTG-context] \externalfigure problem with displaying external images via https://live.contextgarden.net

[Jaroslav Hajtmar]

Hello.
A few years ago I created a PHP application for printing filled forms with PDF background. PHP application is generating ConTeXt source code, that is subsequently translated using the online application https://live.contextgarden.net.
I have now discovered that the application is not functional because the https://live.contextgarden.net application is unable to retrieve the external PDF file from our organization's URL.

Oddly, this source code at https://live.contextgarden.net does not generate a PDF file with the form in the background:

\starttext
 \externalfigure[http://gyza.cz/iapp/opisvysv/498540_SS_16_predmetu_str1_PDF.pdf] % PDF FILE ON OUR ORGANIZATION (SCHOOL) HOSTING
\stoptext

This is despite the fact that the PDF file exists at the URL and the browser is able to display it.

On the other side the source code:

\starttext
\externalfigure[http://hajtmar.cz/iapp/opisvysv/498540_SS_16_predmetu_str1_PDF.pdf] % PDF FILE ON MY PRIVAT HOSTING
\stoptext

or source code:
 
\starttext
 \externalfigure[http://www.pragma-ade.nl/show-gra.pdf] % PDF FILE ON PRAGMA-ADE.NL WEB
\stoptext


without any problems will generate a correct PDF file.

Does anyone know what the problem might be? Why online ConTeXt is not read my PDF file and on other side read another PDF file? What does onlineConText not like?
I need to get my application for printing archive certificates working again...

Thanks.
Jaroslav