1) Inspect the current constraint

-- See the definition of the payment-type CHECK constraint
SELECT conname AS constraint_name,
       pg_get_constraintdef(oid) AS definition
FROM   pg_constraint
WHERE  conrelid = 'organizations'::regclass
  AND  contype  = 'c'
  AND  conname  = 'organizations_organization_payment_type_check';

2 Fix current constraint by updating

ALTER TABLE organizations
  DROP CONSTRAINT IF EXISTS organizations_organization_payment_type_check;

ALTER TABLE organizations
  ADD CONSTRAINT organizations_organization_payment_type_check
  CHECK (organization_payment_type IN (
    'DIRECT_DEBIT_EIGHT_DAYS',
    'DIRECT_DEBIT_THIRTY_DAYS',
    'DIRECT_DEBIT_EIGHT_DAYS_TWO_PERC_DISCOUNT',
    'DIRECT_DEBIT_EIGHT_DAYS_THREE_PERC_DISCOUNT',
    'NOT_DETERMINED',
    'PRO_FORMA',
    'FOURTEEN_DAYS',
    'THIRTY_DAYS',
    'THIRTY_DAYS_TWO_PERC_DISCOUNT',
    'THIRTY_DAYS_THREE_PERC_DISCOUNT',
    'FORTY_FIVE_DAYS',
    'SIXTY_DAYS',
    'NINETY_DAYS',
    'HUNDRED_TWENTY_DAYS'
  ));