Could be mistaken but am guessing that "button" performs an action/function for vMix so am wondering why not do this strait from the script ?

Btw have you searched the forum for Http request or google for vb.net Httprequest

Thank you for your help. I did need to press a button in Companion to control an ATEM. This worked well when I modified it for a button press which is my immediate need, but I could not get a custom variable to change. Do you see anything I could be doing wrong. I commented out the loop to simplify it even further. The variable exists as I copied its name.

Thanks again for your help and posting that simple bit of code is super helpful.

' Prepare for TCP
Dim tcpCompanionIP as string = "127.0.0.1"
Dim tcpCompanionPort as integer = "16759"
Dim client As New System.Net.Sockets.TcpClient(tcpCompanionIP, tcpCompanionPort)
Dim stream As System.Net.Sockets.NetworkStream = client.GetStream()

' Define variables
Dim content As String = "Test_TCP"
Dim numberOfTimes as Integer = 4


' Loop a number of times
' For aNumber as Integer = 1 to numberOfTimes
Dim customVariableName As String = "$(internal:Cam_Transition) "
Dim companionCommand as String = "CUSTOM-VARIABLE " & customVariableName & " SET-VALUE " & content
Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes(companionCommand & Environment.NewLine)
stream.Write(data, 0, data.Length)
' Next

' Close TCP
stream.Close()
client.Close()

Thats what I needed thank you.