Add string variable value to limit value text - how?

Add string variable value to limit value text - how?

Hi all,
I tried to add string variable value in limit value text.
myStringVar value is "TEST STRING"
I try to use placeholders as mentioned in the help.
That is %. So when I put %myStringVar, when limit reached in CEL the text stay as "%myStringVar"?
It's is not "TEST STRING".
I also try with %myStringVar% etc. but no success.

BR,
Milosh