Unable to declare Interface ” async Task MyMethod(Object myObj); ” [duplicate]

Whether a method is implemented using async/await or not is an
implementation detail. How the method should behave is a contract
detail, which should be specified in the normal way.

Note that if you make the method return a Task or a Task<T>, it’s more
obvious that it’s meant to be asynchronous, and will probably be hard
to implement without being asynchronous.

From https://stackoverflow.com/a/6274601/4384