MPOS DA3001 - A connectivity error has occurred and your device can't connect to the server. AX365 Retail

 mpos DA3001 - A connectivity error has occurred and your device can't connect to the server. This may be due to one or more of the following reasons. Contact your system administrator. The server URL typed may have some issues, check for typo errors or if it matches the HTTP protocol of the server. Server can't be reached because it is offline; The Application pool has stopped. Restart the pool and try again; The Server host name can't be resolved because the DNS can't be reached; Server is actively refusing the connection because the port you are using is not allowed through the firewall; The local system doesn't have network connectivity; The local system firewall is blocking outgoing connections. Add a firewall exception for the application. Server is not from the same origin of local system so the request is blocked by Cross-Origin Resource Sharing (CORS)

Solution 

first, check the retail server health by the below link 

https://usnconeboxax1ret.cloud.onebox.dynamics.com/healthcheck?testname=ping

the result should be like this 

PING SMOKE TEST SUMMARY RESULTS

TEST NAME	DATA	RESULT TEXT	TEST STATUS	TEST SEVERITY
Ping	DBCheck	Success	Succeeded	Normal
Ping	RealtimeServiceCheck	Success	Succeeded	Normal

Second

To add Dynamics 365 Modern POS to the loopback exemption list. Run Command Prompt as Administrator and copy-paste the below code. Note: Based on my check on multiple machines, the container name for MPOS is the same across all machines

CheckNetIsolation.exe LoopbackExempt –a -n=microsoft.dynamics.retail.pos_8wekyb3d8bbwe
For more details refer the link belowOriginal reference