Actually, it balks even at the leading digit in the name.
If you won't follow normal naming rules for form fields you have to
(1) Ensure that you put "..." around the entire name.
in the JS code to refer to the field.
But you really never needed to refer to THAT <textarea> by name in that JS code, in the first place.
Just do this:
><?php echo $value;?></textarea>
Notice carefully the quotes around the field name.
Notice that just this
alone specifies the current field! nothing else needed.
Stop using PHP to output complex HTML. Do as I show there: Output the HTML, yes, and then only use the minimal PHP needed to output the contents.
Oh...and upper case letters in event handler names is obsolete. onkeyup and onkeydown are correct.