Hello everybody,
I checked out everything, marking my source with ALERTs. I realized, that the GET method of the WEB-Component causes the error:
The operation < cannot accept the arguments: , [empty-string], [100]
When I switch my PHP-version to 7 on my provider, it works. Turning back to PHP 8 cuases the issue.
Can please somebody help me ?! I need to switch to PHP 8 in 2 weeks.
Thanks in advance, Rolf
Hi @Rolf_Oster,
Have you tried GETing the page using a utility like cURL. It's possible there's an incompatibility in your PHP code that it works on PHP 7 and not PHP 8, and this results in an error message or similar returned that your code in App Inventor isn't handling correctly. You may also want to check that the status code App Inventor sees is 200 (OK) versus say 500 (Internal server error).
It would really help if you provided a screenshot of your relevant blocks, so we can see what you are trying to do, and where the problem may be.
To get an image of your blocks, right click in the Blocks Editor and select "Download Blocks as Image". You might want to use an image editor to crop etc. if required. Then post it here in the community.
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.
Hello Rolf
normally that error would look like this:
[""], [100]
I'm surprised that PHP 7 tolerates a bad argument and PHP 8 does not. What happens if you send two correct values?
Hello,
I solved the problem. First thanks to all the extremely fast answers. Great!
I was using the PHP-function "get_magic_quotes_gpc()", which was depricated and is actually NOT supported (and not necassary any more) in PHP8. This error caused my web-server to return a completely empty answer. However, MIT app inventor doesn't like that and causes the APP exit.
It is unfortunately very confusing to get the error message "The operation < cannot accept the arguments..." because what you then search for is some occurance of "<" in your source. And I still don't know, WHERE app inventor uses the "<" because MY source does not.
However, it was the deprecated function "get_magic_quotes_gpc()"!!!
Thanks again for your help,
Rolf
Edit: My source does have the comparison which doesn't work: 
You must have a math block somewhere with the < operator used. You never showed us what your blocks look like, but an error like that isn't exactly spurious.
Export your .aia file and upload it here.
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