Not up front. What US Vine members pay for is a percentage of the Estimated Taxable Value (ETV) of the item, as determined by Amazon. Your total accrued ETV is calculated on a yearly basis, and can be found on your Account tab toward the bottom under "Taxable value by year". The current year's total is listed there as well as a downloadable itemized report.
If the total is under $600, you will not be sent a 1099-NEC tax document prior to tax time (usually the beginning of Feb). If the total is over $600, you will be able to download your 1099-NEC from your account page. Take this to your tax professional to discuss how it should be filed. Your personal situation will determine what tax bracket and percentage of the ETV total will be taxable. Most new people estimate 30-35% to save up so they have it ready to pay off when the time comes.