Wants to know why I am getting this error while using group by statement in MySQL for project 2?

Error Code: 1055. Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'igclone.users.username' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sqlmode=onlyfullgroup_by NOT able to use group by and that is stopping me to get the output. Please help what I am doing wrong in this.