You are seeing this behavior due to host header check in iDRAC. You need to use FQDN mentioned in iDRAC to access iDRAC without this error. Else you need to disable host header check or ad FQDN you are using as an exception. Refer below link for details [URL]   
v2.83.83.83 was released in April 2022.  We were tasked to upgrade to 2.83.83.83 to correct a vulnerability.  Upgrade worked but can no longer use FQDN to access the idrac.  Can only use the IP address.  When trying to use FQDN we get a BAD REQUEST ACCESS ERROR 400...    I know from a previous thread this has happened with previous earlier versions of the firmware for idrac.  Any possible fixes.?  Really only tried to perform a idrac RESET which did nothing.
Upgraded idrac8 firmware from 2.70.70.70 to 2.83.83.83 and cant no longer use 
FQDN to access idrac