it is all into new install help page, sofollow this instead:
do not follow on reading here, follow phpBB side setup into help install page:
To configure phpBB to set cookie to be available all over the domain (and subdomains), you need to setup cookie domain and path into phpBB ACP
Open phpBB Admin Control Panel, go under
Server configuration -> Cookie settings
Cookie domain value should be set like the domain name is: so if your site domain is as in this example, axew3.com, the correct value to set is:
in this way cookies become available all over axew3.com and any subdomain like mysubdomain.axew3.com.
Cookie path setting should be set as a single fraction slash: /
Change the cookie
If changed cookie setting in phpBB in this way, logout, CLEAN cookies from browser, and re-login.
if on localhost, may leave the value as is. If on subdomain, like myforum.mysite.com, set it as above using only domain name mysite.com)
( Older browsers still implementing the deprecated » RFC 2109 may require a leading . (dot) to match all subdomains, so .mysite.com )
NOTE: if cookie setting changed to be available over all domain because it was not, then all phpBB users may need to re-login using new board’s cookie settings: in this case, you may would like to force all phpBB users to re-login in case they saved their session cookie with a ‘remember me login’. This can be done by accessing phpBB ACP main page: check for option
Purge all sessions
Purge all sessions. This will log out all users by truncating the session table.
Click the Run now button.
Be sure that the cookie setting is correct before to execute these steps, or you’ll be logged out by your board until you’ll not reset to the correct cookie domain!
mysite.co.uk OR mysubdomain.mysite.co.uk, correct setting will be: .mysite.co.uk (while if you are on a subdomain hosting plan like mydomain.myhostingprovider.com, than the setting will be mydomain.myhostingprovider.com, but this is a more rare case)