I plugged my guitar into the VoiceLive Plays thru input but it does not work.
Even though the thru is located under the input section on the VoiceLive Play GTX, it is an output, not an input.
The thru is used in combination with the instrument in. Using the thru removes your guitar from all internal processing including the looper while still using the signal to trigger harmonies. The thru is useful for those who want to use their own guitar processing chain.