parameter expansion & substitution errors

[VMC]

I have this error that uses parameter expansion and parameter substitution, but I get errors. Can you spot the reason for the error?

#!/bin/sh

echo "AQ wE rTy  Ui  Op"

selection="AQ wE rTy  Ui  Op"

choice=${selection// } #remove spaces

choice2=${selection,,} #lower case

echo $choice

echo $choice2

Here's the error: ./x: 5: ./x: Bad substitution

This is just a simple snippet showing the error from a much larger script.

I found the simple error, I just wasn't expecting it.

The original script was showing most of the functions of zenity, found here.