Put a gap/space between the words. Are you sure that you made no mistake while writing down the words?
I just checked my rewards stuff, and I do not get the option to back up my wallet. It is just empty. There are no 24 words. Did they turn off the whole feature? Afaik, currently the only way to back up your wallet is through linking with uphold/gemini or copying your entire brave profile folder from windows file explorer.
Edit:- They removed the feature How to restore Brave Verified Wallet after changing the PC. It works for previous users who already got the code, but new users/browsers do not have the backup 24 words.
Also, it seems even if restore your wallet by the 24 words, you will only get the pending rewards and not the claimed rewards. So, if you had 20 BAt claimed and 3 pending, restoring the wallet, will only get you those 3 BAT.