"The requested URL was rejected. Please consult with your administrator.
Your support ID is: 1353837897337869614"
The response code is a HTTP 200 OK, so that is misleading. The URL of the call is https://<journal_domain>/$$$call$$$/grid/settings/plugins/settings-plugin-grid/manage?category=generic&plugin=customheaderplugin&verb=settings&save=1
This is on OJS 188.8.131.52 and Custom Header plugin version v184.108.40.206. This happens when trying to change both the Header Content and the Footer Content.
The warnings I see in the error logs are:
[php7:warn] [pid 24592] [client 220.127.116.11:56705] PHP Warning: Declaration of CustomHeaderSettingsForm::execute($request, …$functionArgs) should be compatible with Form::execute(…$functionArgs) in /<journal_path>/plugins/generic/customHeader/CustomHeaderSettingsForm.inc.php on line 79, referer: https:/<journal_domain>/management/settings/website
Please let me know if you need more information.