1. Go to Marketing > Affiliates > Affiliate Users and click Add Affiliate (/admin/affiliate/users/0).
2. Leave Is Active on.
3. Choose the Affiliate User from the dropdown of existing customer accounts (accounts that are already affiliates are hidden) and the Affiliate Rule.
4. Optionally pick Affiliate Coupons (multi-select of coupons not yet assigned to another affiliate).
5. Click Save Affiliate.

After saving, the Affiliate Link (https://yoursite/?ref=ID) appears with a Copy button and the Attributed Users panel becomes available. Sprwt sends the customer the "user_affiliates_affiliateuser_create" email every time you save this page — not just on the first save — so re-saving an existing affiliate (e.g. after changing their rule) notifies them again. The affiliate user cannot be changed after the first save (the field becomes read-only). "Invalid User!" means the customer does not exist or is already an affiliate; "Invalid Rule!" means no valid rule was chosen.