To send template messages with variable placeholders, you will first need to create a new template and wait for it to be approved by WhatsApp. This is a manual process that can take an arbitrary amount of time but is usually complete within one or two business days. Templates may be translated in multiple languages, and each language will be reviewed separately, so its fastest to submit them all at once.
You can create templates in the app at Settings → Templates or using the API directly; to get started, we recommend to use the web app, as it provides an interactive template editor that respects all guidelines and limits automatically.
Once your template has been created and approved, you can send messages referring the template using the API, passing in values for the placeholders in the template only.
Please be aware that WhatsApp charges extra for each template message sent. The prices depend on the country of the recipient number.