Time Server

For the Data Transfer between DeDeSales Server and DeDeSales Client, it is necessary that both sides use the same system time. The synchronisation occurs automatically on Android and iOS Devices.
On Windows Devices, however, the behaviour is such that they want to synchronise with the Active Directory Server by default. If the field staff member is not in the VPN or office for a longer time, the synchronisation fails and eventually no Data Transfer is possible due to a too large time difference.
Add in your GPO under
System > Windows Time Service 
at least one public time server that your field staff can reach at any time.