I was able to get past this error today and get my rewards back online… so maybe this can help someone else with the same problem:
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TLDR: When linking a wallet, I would get the error “Your request is still being processed, please wait. Sorry there was a problem processing your request, please try again.”
What I did wrong was: I backed up my Brave Users/Appdata folder then pasted it back in after a reinstall, so Brave would resume where I left off. But Rewards didn’t like that. The file causing problems was “Preferences” in the Default folder. Just leave that file out of the Appdata copy/paste and rewards worked again.
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Background of the error: For the last month or so, I’ve not had a wallet linked or rewards activated. I had to reinstall Windows, and when I reinstalled Brave and tried linking a wallet, I would get this error:

Even just trying to activate rewards by itself (no wallet linking) wouldn’t work.
Reading online, I thought maybe I reached a device limit. Everywhere said to contact support to unlink a device, but I never received any reply. So I just sat here for the last month with rewards off.
But today I decided to try messing around with it again. I uninstalled Brave and reinstalled and, with the fresh install and without touching anything else, I went straight to rewards and tried turning it on and linking wallet, and it worked. My problem was, before reinstalling Windows, I had backed up the C:\Users\username\AppData\Local\BraveSoftware folder, then after reinstalling Brave, pasted those files all back into the directory so my Brave would be right where I left off. Something in that backup wasn’t playing nice with the new install of Brave and wasn’t letting me activate the rewards or link my wallet.
I went file-by-file to find at which point rewards just stopped working and started giving me that error, and it ended up being
“C:\Users\username\AppData\Local\BraveSoftware\Brave-Browser\User Data\Default\Preferences”
Just by leaving that Preferences file out of the copy/paste, I was able to get my Brave back to the way I had it before the reinstall, but also was able to activate rewards and link a wallet again. Only downside, not copying over the Preferences file means you’ll have to go through and redo any Brave settings you had set… but that was easy enough.
It’s largely my fault, as I should have tried a fresh install from the start. But forums had me convinced it was a Brave device limit thing so I gave up. But if anyone else backs up their AppData folder, pastes it back in and gets this error when trying to turn on rewards or link a wallet, hopefully this helps. Just leave that Preferences file out of your AppData copy/paste and Rewards had no problems turning on and linking back up.