When you stand by the charger, does the router appear on your phone when you are searching for Wi-Fi?
If not you may need a Wi-Fi extender closer to the charger. Smart products like the Sync Energy charger work on the 2.4GHz network so won’t show 5GHz networks.
If your router is dual band (see the back of the router) you may need to change some settings to make the 2.4GHz network visible, either by temporarily switching off the 5GHz network until your charger has connected or by creating different network names for the 2.4GHz and 5GHz networks – consult the user guide for your router or speak with your network provider to find out how to do this.