Function not found in API

Support & Bugs
1

Hey guys,
I’m trying to fetch data from the matomo API. I tried via React, I always get error 500 (strict-origin-when-cross-origin). So I tried using a proxy (cors-anywhere), still doesn’t work. With another proxy (cors.sh) I am getting 429- too many requests. I guess with a website running in the browser that might not work requesting the matomo API?

With curl in the command line (Linux Distribution for Windows), I couldn’t reproduce the error, instead I am getting that the function cannot be found in the module API.

curl -X GET ‘https://support.tib.eu/piwik/index.php?idSite=29&rec=1&period=day&date=today&format=JSON&module=API&action=UsersFlow.getUsersFlowPretty&token_auth=…’

Matomo › Error
Matomo 
    <div class="header">
            <h1>An error occurred</h1>
    </div>

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Could it be that the version might be a problem? Afaik currently the version 4.16 is installed and the docs show for version 5.0.
Do you know what might be the issue?
Thanks in regard!