Subject: Thanks for helping us test our app!

Hi <participant's name>

As I mentioned on the phone, we're running some user testing sessions for a new software 
application that is launching soon, and would love for you to be involved.

It will only take around 30 minutes of your time, and you won't need to bring anything to 
the session. 

Here are the details:

Date: <day, dd/mm/yyyy>
Time: <hh:mm>
Room: <room number> (Quiet Room)

I should mention that we will be recording video footage of you using the app - the 
camera will be pointed at the screen, not your face, and the footage will NOT be shared 
outside of the project team - it is purely for the purposes of improving the usability 
of the app.

Assuming you're OK with this, I look forward to seeing you on <day>!

Cheers
<your name>