The more you learn…
“Dues paid by the Department of State for those Members of Congress participating in international organizations. Consists of copies of the purchase order, letters submitted by the participating congressmen requesting payment of dues and a copy of the check.
Destroy when funds are obligated.”
This is from the directives for managing records (A-28-001-08)
FOIA.state.gov/_docs/RecordsDisposition/A-28.pdf