New to the Barista Express

Hi everyone, I recently bought a barista express machine off of eBay (used, like new). For the life of me, I cannot get it to pull even shots. The pressure is within range when I pull and it’s giving me the right amount of grounds for a double shot (~18g). I have a video attached of how it pulls, is this normal? Sometimes it even pulls way less liquid/all dark liquid with no body or crema. Any help is appreciated :)