Use conditional calls and callbacks for implementation-specific functions.\u00a0For example, to provide additional data from the cash register during a transaction, like loyalty data, you use the Additional Data Callback. If the cash register does not handle these calls and callbacks, they will block further processing of the transaction.<\/p>\n
Optional calls and callbacks do not need confirmation from the POS system. For example, the progress callback does not require any action.\u00a0<\/p>\n
These optional extras allow you to integrate specific features from the library:<\/p>\n