Configure and set up single-use promotion codes (SUPC) in Point of Sale CMS.
Salesforce supports SUPC validation outside the Point of Sale Promotion Engine through an SPI. If a code is entered in the Point of Sale app, the code is first checked in the Point of Sale system. If the code isn’t found, it is checked in the merchant’s external system. See Create Promotions in Point of Sale CMS in Salesforce Help.
In CMS, go to Integrations | Custom Connectors.
Click Create.
For Connector Type, select SPI.
For Endpoint Name, select SUPC_PROMOTION_CODE_VALIDATION.
For API Endpoint, provide the external endpoint for validating SUPCs.
For Integration Type, select HTTP_POST.
Specify any JSON headers that must be passed.
Configure the rest of the fields for the SPI. See Point of Sale API, SPI, and Webhook Overview.
Save your changes. 
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