Affiliates' earnings

A few days ago I have recommended a new customer to Theme Forest. He sent his first deposit $100, so I should earn $30 as an affiliate.Unfortunately I can see only $21,60 added as my future withdrawal. A strange thing is that on the graph with affiliate earnings on June I can see $30. Can you explain me this situation? Thanks!

Check your Statement page. Were you charged tax? If so you need to fill out tax info.

Your account here (even if you don’t sell anything) received a payment ($30.00 affiliate earnings) from a US based company (Envato USA Inc.). This payment is subject to US source income tax, in your case 28% Backup Withholding Tax because Envato has no taxpayer infos about you and are forced to treat you as a US author without accurate tax informations.

$30.00 * 0.28 = $8.40 (Backup Withholding Tax)
$30.00 - $8.40 = $21.60