Unable to integrate YouTrack 6.5 with external hub

I've successfully been able to configure upsource to use my external hub, but youtrack refuses to work. I've tried to configure it during the installation, and I get back a JSON response saying something like "hub service [uuid] wasn't found" and gives an error 404. This is despite the fact that a popup successfully opened and asked for permission to integrate with my hub.

I've also tried setting it up using the internal hub and then migrating to the external by using the instructions at https://confluence.jetbrains.com/display/YTD65/Migrating+YouTrack+Data+to+External+Hub. When I do this, I again get a popup from hub asking for permission, but then I get the following message: "Import start is forbidden" and then I only have an option to abort the migration.

I've got upsource, hub, and youtrack all setup behind an apache 2.4 reverse proxy. Each has their own virtual host setup as follows:

<VirtualHost *>
    ServerName youtrack.domain.com

    RewriteEngine on
    AllowEncodedSlashes on

    ProxyRequests Off
    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    ProxyPass / http://centos6.home.domain.com:8082/
    ProxyPassReverse / http://centos6.home.domain.com:8082/
    <Location />
        Order allow,deny
        Allow from all
    </Location>
</VirtualHost>
<VirtualHost *>
    ServerName upsource.domain.com

    RewriteEngine on
    AllowEncodedSlashes on

    RewriteCond %{QUERY_STRING} transport=polling
    RewriteRule /(.*)$ http://centos6.home.domain.com:8081/$1 [P]

    ProxyRequests Off
    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    ProxyPass /~socket.io/ ws://centos6.home.domain.com:8081/~socket.io/
    ProxyPassReverse /~socket.io/ ws://centos6.home.domain.com:8081/~socket.io/

    ProxyPass / http://centos6.home.domain.com:8081/
    ProxyPassReverse / http://centos6.home.domain.com:8081/
    <Location />
        Order allow,deny
        Allow from all
    </Location>
</VirtualHost>
<VirtualHost *>
    ServerName hub.domain.com

    ProxyRequests Off
    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    ProxyPass / http://centos6.home.domain.com:8080/
    ProxyPassReverse / http://centos6.home.domain.com:8080/

    <Location />
        Order allow,deny
        Allow from all
    </Location>
</VirtualHost>

Does anybody know why this is happening? I cannot find a single thing online to help. I've tried restarting both hub and youtrack services, yet nothing helps.