Application integration within a cloud platform system based on declarative callback configuration including registering an application at a vendor portal module to acquire a unique vendor and application identification, declaring callbacks associated with application events, each with a callback type identifier and corresponding data structure, and initiating an API callback by a client module in response to an event, and forwarding the callback to an API Callback Gateway, which verifies the API callback for compliance, encapsulates it with authentication data, and transmits it to a designated callback handler within an ISV infrastructure, processing the callback by the handler, sending a structured response back to the Gateway, which validates and provides the response to a client module, and invoking the cloud platform API using the registered application identifier to trigger the API callback.