Trouble setting a float variable value in Sequencer - (Following a Step by Step in the docs.)

Hello,

I am following this step by step from the docs, and have hit an issue

In “3 - Using Cinematic Exposed Variables” - Step 2, it says “add a key for Default Slot Interp with a value of 1.0.” However, when I try and set a key it reverts to zero every-time.
I have retraced my steps, and am nearly sure I have followed each step correctly.

I am a complete noob when it comes to blueprints, and programming in general … So any help offered would be really appreciated

Many THanks

Paul