Formally or Formerly ?
Your choice!
Formally
Exemple : ‘’You need to dress formally for the party this evening!’’
The words "formally" and "formerly" are often mixed up with each other. "Formally" is an adverb used as a synonym of the word "officially."
Formerly
Exemple : ‘’This building was formerly used as a school.’’
"Formerly" is also an adverb which is used to denote something which happened in the past or previously.