+=item update_customer
+
+Updates an existing customer. Passing an empty value clears that field, while
+NOT passing that key/value at all leaves it alone. Takes a list of keys and
+values as parameters with the following keys:
+
+=over 4
+
+=item secret
+
+API Secret (required)
+
+=item custnum
+
+Customer number (required)
+
+=item first
+
+first name
+
+=item last
+
+last name
+
+=item company
+
+Company name
+
+=item address1
+
+Address line one
+
+=item city
+
+City
+
+=item county
+
+County
+
+=item state
+
+State
+
+=item zip
+
+Zip or postal code
+
+=item country
+
+2 Digit Country Code
+
+=item daytime
+
+Daytime phone number
+
+=item night
+
+Evening phone number
+
+=item fax
+
+Fax number
+
+=item mobile
+
+Mobile number
+
+=item invoicing_list
+
+Comma-separated list of email addresses for email invoices. The special value
+'POST' is used to designate postal invoicing (it may be specified alone or in
+addition to email addresses),
+postal_invoicing
+Set to 1 to enable postal invoicing
+
+=item payby
+
+CARD, DCRD, CHEK, DCHK, LECB, BILL, COMP or PREPAY
+
+=item payinfo
+
+Card number for CARD/DCRD, account_number@aba_number for CHEK/DCHK, prepaid
+"pin" for PREPAY, purchase order number for BILL
+
+=item paycvv
+
+Credit card CVV2 number (1.5+ or 1.4.2 with CVV schema patch)