Buy and track SMS credits
SMS credits pay for text campaigns. Your remaining credits are shown at the top of the Marketing page.
Buy credits
Go to Marketing, click Add and select Buy more credits, choose a pack and pay. During a free trial you'll be asked to upgrade first. See Buy SMS credits.
Track your purchases
Go to Settings > Subscription & Billing and open the Credit purchases tab to see each pack you've bought, how many credits it had, what's been used and its receipt.