Some 3rd party cloud server services are compatible with S2K and some are not.  The simple click to sign up types generally are not compatible.

They need to be able to provide you and S2K full read/write access to the folders that we install and they need to have a static MAC address for the environment.
We do have a company that is familiar with our configuration.  They are not a partner or in any way affiliated with S2K but we do know that they can successfully deploy S2K / Quick Books cloud environments with simultaneous  access for multiple users.
They can be found at the link below:

Another solution that works for some people is QBOX PlusThis service only hosts the QB files - not the QB or S2K software.  This option provides a solution at a much lower cost than the full cloud server type option.
This service will allow the QB file to be located on more than one PC at the same time.  It is similar to drop box but it locks the QB file when in use which prevent multiple users from logging in to the same QB file at the same time.
Here is a link to their web site.