I’m real sorry about that, but there’s a bug with riot’s servers. All you need to do to fix the issue is to go to Collections tab -> Show unowned Champions and then just buy from there.
“Used this service for the first time, at first I was sceptical but within seconds after I placed my order tranthanhan2901 contacted me and was amazing! He was very communicative and finished the job in less than 24 hours! I can definitely recommend him as your booster :)”
“Cigar has to be one of the best players I've ever met, he was professional, kind and knowledgeable. Beyond what I was expecting and truly great service. Anyone who gets him will be satisfied in everyway. A wonderful experience thank you”
“maroc16062002 has over delivered on the service, we had great fun playing and he's been very knowledgeable about the game. would 100% recommend him to people that are looking to climb and gain knowledge about the game”