You can disable direct payments (prepayments), so you can no longer receive prepays from SkyPrivate members, by logging into your SkyPrivate account and going to Settings ⇒ Payments ⇒ Settings ⇒ Direct payments (prepays).
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There, you will have the option of receiving direct payments. If you would like to have it disabled, click "no" and after that, click on the "Save Changes" button.