Issue creation by rest doesn't work (probably no screen found)

[Pietro Lehmann]

I'm 100% sure that my request is Correct,

I'm 100% sure that the Screen the request uses at least contains description and summary. 

Creating Test Issues with the GUI works perfectly fine. 

I work with a Jira-Server.

I'm trying to create X-Ray Tests with the rest API. But it always returns me those errors: 

Below you see the fields i add to my request. Putting them in "" makes no difference. 

"fields": {
    "project": {
        "key": "XT"
    },
    "issuetype": {
        "name": "Test" // aktueller issue --> issue.fields.issuetype.id
    },
    "summary": issue.fields.summary, // Zusammenfassung => nok
    "description": issue.fields.description, // Beschreibung => nok

    customfield_10703: {
        value: "Manual" // Testtyp => nok
    },
    customfield_10707: { // Manuelle Testschritte => nok
        steps: [{
            index: 0,
            step: "Step 1",
            data: "input Data1",
            result: "result"
        }]
    },
    customfield_11109: "jira.geoinfo.ch/browse/" + issue.key, // Test-Link => nok

}

When i remove all the Xray Fields and create an Issue in a standard Project with just description and summary i get those errors: 

It seems like I'm not able to create any Issues. But other API requests like api/2/projects work perfectly fine.