WeChat uses a local network back up or restore your chat history. No cellular data will be used.

Check your network connection:  Make sure your phone and computer are connected to the same network (router, personal hotspot or wireless card) to transfer the data. Only local networks are used during this process, so no cellular data will be used.

Check your firewall settings:  On the computer, check whether WeChat for Windows/Mac has been blocked by the firewall. The back up/restore feature may not be available in complex network environments due to a firewall or restrictions put in place by the network admin.