The most common cause is a card decline, not an account restriction. Banks sometimes flag first-time Branvas charges as fraud (Capital One especially), or the charge exceeds the card's credit line. The fix: call your bank to approve the transaction, then retry the payment. If it keeps failing, message support and we can check the exact decline reason with Stripe (more on declines: My payment was declined or failed - what do I do?).
Things that do not block sample orders: there is no limit on the number of sample orders, no minimum quantity, and no plan requirement. Sample orders are available on every plan, including Free.