You may want to consider Searching Before Posting in the future. This is something discussed on a regular basis and each time people are given the same response.
There’s a reason, just one you don’t recognize or agree with. The system detected unusual behavior that indicated you might be abusing Rewards system or violating Terms in one form or another. That’s why people get flagged. It doesn’t mean you actually did something wrong, but your activity was enough to trigger antifraud and pause your earnings.
And as to what to do, you’d even have seen what to do in the FAQ over at Flagged account
In any case, you can wait for it to automatically remove the flag (which can take over a year), or you can submit a Rewards Support Ticket at https://support.brave.com/hc/en-us/requests/new?ticket_form_id=360001302431