Jenkins create Folder with REST API in groovy skript

i am trying to create a Folder in Jenkins using a groovy script. For that i use an REST API call. My starting point is was basically a curl command:

curl -XPOST "http://userName:YourApiToken@JenkinsURL:Port/createItem?name=FolderName&mode=com.cloudbees.hudson.plugins.folder.Folder" -H "Content-Type:application/x-www-form-urlencoded" 

I got this from and found later out that it also works if you put the user into the URL. Using this line in the Windows cmd works perfectly and generates me a new Folder in my Jenkins.

Now i try to do the same thing but from a groovy script. For that i use the following code:

import*  def post = new URL("https://userName:YourApiToken@JenkinsURL:Port/createItem?name=FolderName&mode=com.cloudbees.hudson.plugins.folder.Folder").openConnection(); post.setRequestMethod("POST") post.setDoOutput(true) post.setRequestProperty("Content-Type", "application/x-www-form-urlencoded") def postRC = post.getResponseCode(); println(postRC); if(postRC.equals(200)) {     println(post.getInputStream().getText()); } 

I got this basically from Groovy built-in REST/HTTP client? (i have heard apache Http is deprecated)

Long story short i did not manage to create a folder with the given groovy script. I always get an 403 response (I run the script from windows cmd and inside jenkins with the script console). I also played around with Jenkins-crumb but that seems not necessary because the above cmd command already worked.

So the question is does anyone know what i am missing? why is the groovy script not working but the curl command is? Or has anyone a different approach on how to generate a Folder in Jenkins from a groovy script?