1. Go to Marketing > SMS > Buy Credits (the SMS Wallet page).
2. Choose a pack: Starter $1.00, Essentials $50.00, Growth $75.00, Business $100.00, Scale $250.00 (marked Most Popular), Pro $350.00, Enterprise $500.00, or type your own amount in the Custom card (minimum $50.00) and click Continue. Each pack shows an estimated number of messages ("~N SMS") based on your rate.
3. Click Add $X credit, then confirm "ARE YOU SURE YOU WANT TO ADD $X IN SMS CREDITS?".

The card on file for your Sprwt account is charged the amount plus a 3.5% processing fee; only the base amount is added to the wallet, and only after the charge succeeds. The page then shows "SMS Credit Added Successfully" and updates the balance. Custom amounts under $50 are rejected with "Minimum custom amount is $50.00".