How to call a method after a delay in android using rxjava?

This is how I would do it:

    Completable.timer(5, TimeUnit.SECONDS, AndroidSchedulers.mainThread())
        .subscribe(this::getTransactionDetails);

A Completable represents a deferred computation with no value but an indication for completion or exception. The static method call timer() returns a Completable that signals completion after the specified time period has elapsed, and the subscribe() call will mean that the method getTransactionDetails() will be called on the current object when the timer fires. By supplying a Scheduler as the last argument to Completable.timer() you control which thread is used to execute getTransactionDetails().