-For Customers (cust_main):
-'CARD' (credit card - automatic), 'DCRD' (credit card - on-demand),
-'CHEK' (electronic check - automatic), 'DCHK' (electronic check - on-demand),
-'LECB' (Phone bill billing), 'BILL' (billing), 'COMP' (free), or
-'PREPAY' (special billing type: applies a credit - see L<FS::prepay_credit> and sets billing type to I<BILL>)
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-For Refunds (cust_refund):
-'CARD' (credit cards), 'CHEK' (electronic check/ACH),
-'LECB' (Phone bill billing), 'BILL' (billing), 'CASH' (cash),
-'WEST' (Western Union), 'MCRD' (Manual credit card), 'CBAK' (Chargeback), or 'COMP' (free)
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-For Payments (cust_pay):
-'CARD' (credit cards), 'CHEK' (electronic check/ACH),
-'LECB' (phone bill billing), 'BILL' (billing), 'PREP' (prepaid card),
-'CASH' (cash), 'WEST' (Western Union), or 'MCRD' (Manual credit card)
-'COMP' (free) is depricated as a payment type in cust_pay
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