The Flow Chart that follows utilizes a chain of 3 messages and a suggested time sequence between messages. Ultimately the organization utilizing Transaction Validations process can configure the technologies used, the number of messages to be sent and the timing of the messages and decisions.

Best practices related to the processes are somewhat dependent upon the risks related to the transaction. The method of transmitting the message and receiving the reply message can be configured and tailored to the origin of the transaction. IE from a mobile device, SMS would be the first choice. Multiple technologies could be combined as an example the final message might utilize all technologies.
The content of the message is also configurable, the goal is to identify the transaction while staying far away from sensitive data like card numbers.