Known issue that has been persistently hard to identify. Various workarounds that work for some users and not others. Posting the information below. If the suggested workarounds do not work for you, try digging into the GitHub issue reports and the linked topic. Other things identified there that may work in your case. You should probably keep track of the issue report and community topic linked below. Any updates will probably be posted in either of those places.
ISSUE: Whatsapp Not Working
Workaround:
- Disasble Honey extension if installed (other extensions too have been culprit)
- Disable
Use hardware acceleration when availableatbrave://settings/system - Close and relaunch Brave
Topic Reference: Whatsapp Web is not working
Most active Community topic which has other workarounds (along with the GitHub issue report below) that also worked for some users
Brave GitHub Issue Report (Source):
Web.whatsapp.com fails to authenticate and returns “Make sure you computer has an active internet connection”
Above Information from: User Solutions: Brave Release 1.43.x