On Sunday, in Liverpool vs United, on 93rd minute Mata was given offside, both the refs had given offside (they showed offside signs and ref whistles too). Alisson caught the ball and took a drop-kick (kicking the ball through his hands) which assisted Salah and resulted in the goal.
As per my knowledge, an INDIRECT FREEKICK is awarded for an offside. So how did Alisson take it as drop-kick and even after whistling and showing offside sign, how was he allowed to take it? (Ref did not show advantage).
So my question is, is drop-kick allowed for an offside if it is in the box?