According to this post :
Input Data Field Name should be the orange text - the binary field name from your previous node (e.g., data, speech.mp3, or whatever is shown in the Binary tab).
If in your case is not working, maybe change the actual name of output from form to something else than speech.mp3 since the extension is mpga anyway… and maybe it’s a conflict, or where do you upload it it requires specific format… 