Okay, so if your certificate is expired, we know this won’t work within the applications (specifically iOS) so we are only discussing web based access.
I looked up OpenWRT/lighthttpd and am fairly confident you can add the CORS header by doing the following:
1) Open the file /etc/lighttpd/lighttpd.conf on the device by using nano or vi.
2) Add the following code:
setenv.add-response-header = ( "Access-Control-Allow-Origin" => "*" )
If this doesn’t work, feel free to send the screenshots in Hungarian. The general error should be apparent however it is likely CORS related issues.