-- Convert prepaid SMS balance from IRT to credit units.
-- Previous billing: 400 IRT per 64-char segment.
-- New model: balance is SMS credits (1 credit = 1 segment); top-up at 500 IRT/credit.
-- Preserve existing prepaid capacity: IRT / 400 → credits.

UPDATE businesses
SET sms_balance = sms_balance / 400
WHERE sms_balance > 0;

COMMENT ON COLUMN businesses.sms_balance IS
  'Prepaid SMS credit units. 1 unit = one 64-character segment per recipient. Top-up adds floor(IRT / 500) credits.';