Open the affiliate under Affiliate Users, switch Is Active off and click Save Affiliate. The affiliate moves to the Inactive tab (its KPI card subtitle reads "Paused or ended partnerships"), and from then on orders from their attributed customers no longer generate commissions ("Affiliate provided is not active"). Existing unpaid commissions remain in the report and can still be paid or rejected. Their dashboard shows an Inactive badge but stays accessible. Switch Is Active back on to resume.