Variables in datasouce Display block

Firstly my apologies as I am a complete Noob, we all have to start somewhere.

As part of the display block tutorial you demonstrate replacing text with a variable. When I try and do this I get an error. I have nailed this down to when I am prompted to enter the variable if I use text i get the error, but if i enter a number then it works.
I guess either the JSON APL is reading my variable as a integer when it should be a string. I have no idea how to correct this.

What error do you get ?