Autohotkey Send Dynamic Key

I'm trying to create a script with a user-configurable hotkey

I can bind to the dynamic hotkey, but I can't seem to send a hotkey.

Here is a simple script illustrating the problem

#Persistent
#SingleInstance, Force
btn1 := "F1"
btn5 := "F5"
Hotkey, %btn1% Up, stop1
Hotkey, %btn5% Up, stop5

stop1() {
  MsgBox f1 was released, sending f1 dynamically
  Send {%btn1%}
}

stop5() {
  MsgBox f5 was released, sending f1 statically
  Send {F1}
}

If I press F1, it triggers start1, and attempts to send F1 dynamically, as it's set in the header of the script. Nothing happens.

If I press F5, it triggers start5, and sends F1 statically. If your focused program uses that binding, the command is executed.

In my actual script, I need to be able to Send {%btn1% up} and Send {%btn1% down}