A had the same error, following your instruction and the error show up
(using the function bt 14 for log in the panel)
(using your instruction for curl -v https://brandnew.aapanel.com)
ping is ok (ping brandnew.aapanel.com -c 5 - ping google.com -c 5)
(using curl -v http://brandnew.aapanel.com)
(error after log on panel)
all my applications runs behind aapanel returns error 403, pls save me!