Complex sentence: Goodwill missions of state are usually carried out or overseen by the head of state and does not necessarily involve diplomatic credentials outside of a letter of presentation or credence, however some states do issue credentials that include diplomatic immunity for their goodwill ambassadors such as Haiti.
Split into simpler sentences: Goodwill missions of countries are usually carried out or overseen by the head of state, and do not necessarily involve diplomatic credentials outside of a letter of presentation (or credence). However, some states do issue credentials that include diplomatic immunity for their goodwill ambassadors such as Haiti.