@Elena *********
problem? yes, possibly.
Personally, I used an actual flight number and proposed date, but no, I had not made any booking. Same with accommodation. I just gave the details of a hotel I like, but hadn't booked it.
That was Australia.
Frankly, I have no idea why they want proof of these details, since there's no requirement to actually use the visa - unless perhaps it's soft power and they want to ensure the application is legit and ties in with the booked course.