SMS billing flow is a common process used in verifying a customer. The SMS feature of the mobile phone is utilized to verify authenticity of the customer before a payment is made. According to this process, the customer should send or receive SMS to verify authentication of the payment. Different types of SMS billing flow are available: MO SMS Customer should send keyword from the SMS on their phone. MT SMS - Customer should get SMS on their phone. Handshake MT Customer must reply to the SMS received. MSISDN Mobile number of the customer should be used.