Whenever Quickbooks POS do not connect the server some following reasons.
It might be server setting is not set to multi-user mode
Network connection error
Dynamic IP used in the setting of Quickbooks pos server etc.
If you want to resolve this issue. Make a call on 844-888-4666 to get Quickbooks POS technical support or visit website if you want to get more information.More details: Get Quickbooks POS Technical Support Whenever POS Will Not Connect To The Server.