There are two things to keep separate: what you invoice your buyers, and what AllEasyWay invoices you for boosts.
Your sales. Payment happens directly between you and the buyer, off the app. As a professional, it is up to you to issue invoices to your customers and to apply VAT according to your tax regime and country.
Your boosts. Spotlight and Premium are paid by in-app purchase via the App Store or Google Play. Billing and VAT for those purchases are handled by the store, which provides your receipt.
AllEasyWay takes no commission on your sales between users. For tax questions specific to your situation, speak to your accountant; our terms of sale describe the applicable framework.