did you override the Resolve method of IPropertyConvertorProvider - if you post your code i can help to see what is missing,

I have my Property Converter :

public class TitleBodyPropertyConverter : IPropertyConverter
{
   public IPropertyModel Convert(PropertyData propertyData, ConverterContext contentMappingContext)
   {
      throw new NotImplementedException();
   }
}

which I am not completely sure how to map my property to the content api property and because of that I can't implement the Resolve method. For now the Resolve method is empty:

public class TitleBodyPropertyConverterProvider : IPropertyConverterProvider
{
    public IPropertyConverter Resolve(PropertyData propertyData)
    {
        //if (propertyData == yourPropertyModel)
        //{
        //    return yourPropertyConverter;
        //}

        return null;
    }

    public int SortOrder { get; }
}

You seems to have taken the right approach 

Have you created the PropertyModel to be return from IPropertyConverter

YourPropertyModel : PropertyModel<IList<T>, PropertyList<T> ?

and then in  Resolve you can check if propertyData is of type PropertyList<T>

It should work.

Thank you @Muhanned for your response. 

With the latest version of the Content Delivery API it's enough to have your custom property model YourPropertyModel : PropertyModel<IList<T>, PropertyList<T>  and it works.  No need for the IPropertyConverter to be implemented. At least in my case.

I had a corrupted DB and that's why nonthing works what ever I tried.