Testrail Api (old) after upgrade to v 3

Hi,
In your documentation you wrote, that the old version is still in place, although it will not be supported for new features.

I wrote a method in C# for writing back some testresults to testrail.
After the upgrading to v3 I got the error
Missing argument 1 for DropdownField::get_validation_rule(), called in C:\inetpub\testrail\app\controllers\miniapi.php on line 685 and defined

Here is the url:
https://testrail.xitaso.com/index.php?/ … 4fccc4a4d8

and here are the parameters that were passed:
status_id=1&comment="Success"&version=&elapsed=0&defects=&assignedto_id=1&custom_browser=5

The request header contains Accept: application/json and ContentType = "application/x-www-form-urlencoded" .

So are there any changes, or did I miss something?