You're customizing your video's thumbnail and you came across the error "Custom thumbnail size [dimensions of your thumbnail image] must match the size of the video [dimensions of your video]."
It's an easy fix!
Simply put, your thumbnail must exactly match your video's dimensions. For example, if your video is 1080x1920, your thumbnail should be the same.
Just click the pencil icon. Then, use our editor to crop or resize it.