Anne-Marie was singing "Don't Play" with KSI and Digital Animals on stage.
https://www.youtube.com/watch?v=qjQjxpnwVZw
The singer had began the performance by singing a verse from her Little Mix collaboration "Kiss My (Uh Oh)" from in front of heart at the top of a small suitcase. While walking down the stairs, Anne Marie missed a step, tripped and landed on the stage a few steps below.
After finishing off the performance, Anne Marie later tweeted “Didn’t need my left ankle anyway".