I am sorry to know you have encountered any difficulties with running the API tests from cmd and will be happy to assist you in sorting this out.
It seems that you tried to execute the tests via the command line using the ArtOftest.Runner - this, however, is the runner, which recognizes the tests in a Test Studio Web&Desktop project (web, wpf, performance tests). The API project and tests has completely different structure and thus they need different type of runner and arguments. You can see in the referred article that the API testing runner is called Telerik.ApiTesting.Runner and can be found in this folder C:\Program Files\Telerik\Test Studio\Bin\ApiTesting\runnerconsole.
Please, give a try to the command line execution using the correct runner and let me know if you still are facing any issues with the test runs.
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