Is that all? What should I do next?
You just need to wait until eventually they accept your request. Sometimes it takes a few days, sometimes it takes a few weeks and sometimes it takes even months, but within this year they will accept the domain request. Eventually you’ll see that your domain will contain the right nameservers when they accepted it, so you can then add it on your hosting account!
I believe I had encountered rejection once
Well, they also have to check whether the domain you’re registering abides by their Terms of Service. If it isn’t the request will be denied.