Creating an entitlement

function create_entitlement (user_id, merchant, product, offer = null, notification_url) {
    // *Always* use this endpoint prefix for the Bango Resale API.
    const base_url = "https://resale.api.bango.net";

    // This is what we're trying to find.
    let entitlement = null;

    const request_body_params = {
        // Your unique identifier for the user.
        customerIdentifier: user_id,

        // Identifier for the merchant providing the service,
        // supplied by Bango.
        merchantAccountKey: merchant,

        // Identifier for the product representing the service,
        // supplied by Bango.
        productKey: product,

        // Identifier for the offer associated with the service,
        // supplied by Bango. (Use null, or omit, if no offer key applies)
        offerKey: offer,

        // Your custom URL: the Bango Platform POSTs asynchronously
        // to this URL on changes to the entitlement.
        notificationUrl: notification_url,

        // See API reference for more parameters.
        // You could use your own entitlement IDs if you want, for example:
        // entitlementId: get_entitlement_id(...);
    };

    try {
        // POST UTF-8 JSON to the Bango Resale API and parse the JSON response
        let response = rest_client_call({
            method: "POST",
            url: base_url + "entitlement",
            headers: {
                "Authorization": get_authorization_header(),
                "Content-Type": "application/json",
            },
            body: make_json_string(request_body_params),
        }).from_json();

        // The responseCode tells us the result.
        switch (response.responseCode) {
            // Success: entitlement is created and ACTIVE
            case "OK":
                entitlement = response;
                break;

            // More to do: The reseller must take action
            case "CLIENT_ACTION_REQUIRED":
                // This response parameter tells us what we need to do.
                switch (response.parameters.action) {
                    case "NAVIGATE_TO_URL":
                        // Send the user to a particular web page
                        // to complete a merchant-defined process.
                        // request_body_params must include notificationUrl
                        // to ensure you receive notification of service
                        // activation asynchronously.
                        redirect_device_to({
                            url: response.parameters.url,
                        });
                        // entitlement is created and PENDING
                        entitlement = response;
                        break;

                    default:
                        // Unrecognized action.
                        // Check the documentation again.
                        throw "Unrecognized client action";
                }

                break;

            // Failures
            // These may indicate issues in your code, not the Bango Platform.
            case "BAD_REQUEST": // Invalid request
            case "UNAUTHORIZED": // Check your credentials
            case "NOT_AVAILABLE": // Unable to activate this service
            case "ALREADY_EXISTS": // You tried to reuse an entitlement ID
            case "TOO_MANY_REQUESTS": // Request limit reached: try again later
                throw "Unable to create entitlement";

            // Bango Platform issues
            // These likely indicate transient problems.
            // In production code, you might want to try the request again
            // after a delay, ultimately falling back to an error state.
            case "INTERNAL_ERROR":
            case "SERVICE_UNAVAILABLE":
                throw "Bango Platform unavailable";

            // This might indicate Bango has added a new response code.
            // Check the documentation again.
            default:
                throw "Unrecognized response code";
        }

    } catch (exception) {
        // Production code might want to notify the reseller in some way,
        // and/or log full details of the exception for later analysis,
        // and degrade gracefully for the user.
        output("An error occurred!");
        output(exception);
    }

    // null if entitlement not created.
    // If created, will have an entitlementId, status, and other properties:
    // see API reference.
    return entitlement;
}