The license key can be applied as every jsreport configuration
https://jsreport.net/learn/configuration
You have multiple ways, but the easiest is typically to use jsreport.config.json configuration file and add
"licenseKey": "XXXX"`When you follow azure functions tutorial, you should add it to both jsreport.config.json and prod.config.json.
The second puplar option is to use environment variables to configure jsreport. In the case of the azure functions, you can set environment variables in azure portal in the Configuration/Application Settings menu. There you can add licenseKey with proper value.