You should be a subject to VAT or own a small business to receive payouts from CopeCart for your Vendor/Affiliate activity. However, it depends on your business type what payout amount—net or gross—you will receive.
You can provide us with your VAT ID or tax number in Account Settings: https://copecart.com/account/edit
If you are a subject to German VAT (i.e. you run a business in Germany), you will receive payouts in gross amount so you can pay back the corresponding VAT rate to German tax office.
If you run a small business in Germany (i.e. your previous calendar year turnover is less than 22,000 € and prognosed turnover for this year is less than 50,000 €), you will receive payouts in net amount because CopeCart pays the applicable tax for you.
If you possess a VAT ID in any of EU countries (i.e., not Germany), you will receive payouts in net amount.