C# MVC Controller cannot get double values from POST request

Question

Can somebody help me with this mysterious problem? For example if the user inputs the value of the field called "Betrag" (amount) to lets say 0.03 in the C# MVC Controler api in the parameter of the Post method the value of the field "Betrag" will be 3 not 0.03.

     postForm(formValues: any): Promise<any> {
    const formData = this.prepareFormData(formValues, undefined);

    return this.http.post('/buchung/buchungspeichern', formData).toPromise();

  }

  prepareFormData(formValues, belegnrAbweisung: any) {
  formData.append('Buchung.Betrag', JSON.stringify(formValues.get('betrag').value);
  console.log(formData.get('Buchung.Betrag')) //OUTPUT: 0.03

  return formData;
 }

API

    [HttpPost("BuchungSpeichern")]
    [ProducesResponseType(typeof(bool), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status400BadRequest)]
    [ProducesResponseType(StatusCodes.Status500InternalServerError)]
    [Authorize]
    public async Task<ActionResult> BuchungSpeichern([FromForm]BuchungSpeichernCommand command){
  ...
   }

      public class BuchungSpeichernCommand
{
    public BuchungCommandDto Buchung { get; set; }
}

public class BuchungCommandDto
{
    public double? Betrag { get; set; }
 }