Azure Form Recognizer documentClassifiers training

Hi ,

I want to train my Azure Form Recognizer custom classification model. According to the REST API documentation. However building the model with the following code fails with the following error message:

"TrainingContentMissing: Training data is missing: Could not find any training data at the given path."

The training source is uploaded in the Azure Blob Storage ad the right prefix folders. If I use the Form Recognizer Studio, it finds the training source and asks me if it should label it according to the folder name.

https://westeurope.api.cognitive.microsoft.com/formrecognizer/documentClassifiers:build?api-version=2023-02-28-preview


Body:
{
  "classifierId": "customClassificationModelVersion4",
  "description": "",
  "docTypes": { 
 "Label1": {
      "azureBlobSource": {
containerUrl": "[CONTAINER SAS TOKEN, inluding the containername]",
        "prefix": "training/Label1/"
      }
    }, 
 "Label2": {
      "azureBlobSource": {
        "containerUrl": "[CONTAINER SAS TOKEN, inluding the containername]",
        "prefix": "training/Labe2/"
      }
    }, 
 "Label3": {
      "azureBlobSource": {
        "containerUrl": "[CONTAINER SAS TOKEN, inluding the containername]",
        "prefix": "training/Label3/"
      }
    }, 
 "Label4": {
      "azureBlobSource": {
        "containerUrl": "[CONTAINER SAS TOKEN, inluding the containername]",
        "prefix": "training/Label4/"
      }
    }
  }
}