supplementary
adjective
uk/ˌsʌplɪˈmentəri/ us( US also supplemental)that is provided, needed, or asked for in addition to something else:
Also included will be supplementary liability insurance, often up to $1 million, as protection against claims from any third parties.
A supplementary budget may be needed to cover the cost of repairs.
He is quoted as saying he would not contribute to what he called an unfair supplementary business tax.
We will issue a brief supplemental report when these steps are completed.