FallbackDeliveryApiJsonTypeResolver.cs

public class FallbackDeliveryApiJsonTypeResolver : DeliveryApiJsonTypeResolver
{
    public override JsonTypeInfo GetTypeInfo(Type type, JsonSerializerOptions options)
    {
        var typeInfo = base.GetTypeInfo(type, options);
        if (typeInfo.PolymorphismOptions != null)
        {
            typeInfo.PolymorphismOptions.UnknownDerivedTypeHandling = JsonUnknownDerivedTypeHandling.FallBackToBaseType;
        }

        return typeInfo;
    }
}