For Gravity :
https://www.youtube.com/watch?v=gtU1_BvnssU
https://help.usaepay.info/merchant/guide/customers/customer-database/
For Fattmerchant:
https://fattmerchant.wistia.com/medias/yjmx1yo5nm
SmartServ Inc.
For Gravity :
https://www.youtube.com/watch?v=gtU1_BvnssU
https://help.usaepay.info/merchant/guide/customers/customer-database/
For Fattmerchant:
https://fattmerchant.wistia.com/medias/yjmx1yo5nm