WEBHOOK SUBSCRIPTIONS ARE LIMITED TO 5 PER PJMID.
For more information on PayJunction account structures, see the PayJunction Account Structures guide.
The answer to this question depends on the type of application you have.
If your software is a native application, i.e. it does not work through a web browser, or does not have communication with a backend cloud service, then you'll need to use the Polling API to avoid being blocked by the end-users' firewall. No firewall configuration changes should be necessary with the Polling API, as it uses standard HTTPS to communicate with our cloud servers.
However, if your software is SaaS (software as a service) and works through a backend web service, the Webhook API is recommended to reduce traffic and ensure that transaction data is recorded even if there is a failure on the local device.
A combination of both is also possible. The Polling API can be used for the local app to check for transaction status, while the Webhook API can be used to report to an online server for backend data storage and redundancy, or a data translation service such as Zapier.
Still unsure which you need to use, or which might work best with your current platform? Open a ticket and we'll assist you.