Running a client in-house proprietary application capable of conducting a user credit check
Running third-party trading app (e.g. Autobahn FX)

The FX Trader clicks button to book a trade in the third-party trading app (e.g. Autobahn FX)
The trading app executes an interop action to the client in-house proprietary credit check application to check the trader's credit limit. If this check indicates the limit has been reached, the trading app presents a rejection dialog as a standard error dialog box with an informational message which may be a standard message (e.g. "Credit Limit Reached") or may include an interop link/action (provided by the credit check application) to resolve the limit breach.

Point-to-point RPC invocation.
Current FDC3 API proposal doesn't define response message for "open" and "send" methods as they both returns Promise<void>:
https://github.com/FDC3/API/blob/master/src/interface.ts#L66
https://github.com/FDC3/API/blob/master/src/interface.ts#L34

Browser not supported