AJAX calls can make a website dynamic, but they can also pose unique problems in terms of automation. When using third-party APIs or services, it is imperative to test whether the application can effectively communicate with them while handling errors that arise - network outages, rate limiting and invalid responses should all be covered when testing these external services.
Additionally, an application must manage authentication and authorization to securely access external services. Error handling and logging should help diagnose issues with third-party APIs or services; while regular testing will help to ensure that its operation continues as designed should changes be made to those external APIs or services.