Retrieving Formview ID value with linkbutton

Hello - I am attempting to insert the ID from a Formview into the ID column of a datatable using a linkbutton. I am able to insert the firstName and lastName, but the ID is coming over as zero (0).

I'm not sure that my coding is correct for this, as it's the first time I've attempted this with a formview control. Specifically, I don't know if I'm using the linkbutton's CommandArgument and OnCommand correctly.

I have OnCommand equal to the code-behind Sub. And I have the CommandArgument equal to the ID (using Eval).

In the code-behind I am declaring the ID like this:
Dim ID As Integer = FormViewTherapist.DataKey(e.CommandArgument)

Again, I'm not sure if this is correct. I'm getting zero for the value instead of the true ID.

Thanks for your help!

FORMVIEW CONTROL ON ASPX PAGE
 
<asp:FormView ID="FormViewTherapist" runat="server" DataKeyNames="therapistID" DataSourceID="SqlDataSourceTherapistDetail">
<ItemTemplate>
<asp:LinkButton ID="LinkButton1" runat="server" CssClass="selectlink" OnCommand="AddToClinicianListFromClinician" CommandArgument='<%# Eval("therapistID") %>'>Add to Selection</asp:LinkButton>
<asp:Label ID="firstNameLabel" runat="server" Text='<%# Bind("firstName") %>' CssClass="big" />
<asp:Label ID="lastNameLabel" runat="server" Text='<%# Bind("lastName") %>' CssClass="big" />
</ItemTemplate>
</asp:FormView>
 
CODE BEHIND (VB)
 
Dim ID As Integer = FormViewTherapist.DataKey(e.CommandArgument)
        Dim firstNameAdd As Label = CType(FormViewTherapist.Row.FindControl("firstNameLabel"), Label)
        Dim lastNameAdd As Label = CType(FormViewTherapist.Row.FindControl("lastNameLabel"), Label)
        Dim firstNameAddText As String = firstNameAdd.Text
        Dim lastNameAddText As String = lastNameAdd.Text
 
        AddClinicianTable(ID, firstNameAddText, lastNameAddText, CType(Session("CliniciansTableSession"), DataTable))
 
        Me.RepeaterClinicians.DataSource = CType(Session("CliniciansTableSession"), DataTable).DefaultView
 
        Me.RepeaterClinicians.DataBind()
        Me.DataListOfficesTherapists.DataBind()
        ID = CInt(ID)
        firstNameAddText = ""
        lastNameAddText = ""
 
    End Sub

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