In Json is it ok to have a single endpoint with an outer wrapper around a dynamic payload, or is this simply not recommended? (sort of late-binding)

For context I am using vb.net but the concepts remain the same. This is a submission API for dozens of different sample sheets. As such I would like to have the one main endpoint and use 2 properties that define what "object" the internal payload resolves too. I would have thought this would be a fairly std paradigm as I have used it many times in the past when the transport format was xml, but I have not found much mentioning it when it is Json.
As an example; the wrapper class:

    Public Class Submission
        Public Property AgreementCode As String
        Public Property SampleType As String
        Public Property SampleTypeVersion As Integer
        Public Property Details As Object 'Note!
    End Class

And an inner class: (one of many)

    Public Class TubeV2
        Public SampleNumber As Integer
        
        Public SampleName As String
        Public Property TubeName As String
        Public Property AdditionalComments As String
        Public Property SexAtBirth As String
    End Class

The server-side code that makes this all work is;

        
        
        Public Overloads Function UploadSubmissionWithPayload( ByVal value 
              As WebApiNoMVC.Model.Submission) As HttpResponseMessage
            If value.SampleType = "Tube" And 
                           value.SampleTypeVersion = 2 Then

                Dim oTube As WebApiNoMVC.Model.TubeV2
                Dim objs As List(Of WebApiNoMVC.Model.TubeV2) = 
                             value.Details.ToObject(Of List(Of WebApiNoMVC.Model.TubeV2))()
                For Each oTube In objs
                    'all values are now available
                Next
    elseif etc etc

And finally a concrete json example;

       {"AgreementCode":"ABCDEF2297321","SampleType":"Tube","SampleTypeVersion":2,
            "Details": [
                {
                    "SampleNumber": "1",
                    "SampleName": "Dido","TubeName":"Tube1",
                    "SexAtBirth": "F"
                },
                {
                    "SampleNumber": "2",
                    "SampleName": "Adsy", "AdditionalComments":"Trans",
                    "SexAtBirth": "U"
                }
               ]
            }

I really like this as a paradigm but have a feeling this is just no longer the way "things are done".
Is anyone able to either confirm this is ok as a design pattern, or conversely highlight why it is a really bad idea?
So far the main issue raised is that as the internal json objects are not part of the endpoint and so they are not automatically described using YAML/Open API, but as they could be easily described (and disseminated) using Json schema I'm not sure how critical a drawback this is, if it is at all.