Store Locator Plugin Guide
Error! Geocoding Service, You must use an API Key to authenticate
You are using the Store Locator plugin and you have added your API keys properly but still, somehow the plugin map is reporting such an error, there maybe a couple of reasons behind this, the most important is the WordPress cache plugin, most of the times the user doesn't refresh the cache and this error is being served even after adding the API Keys properly.
LiteSpeed Cache Plugin
In case you are using the LiteSpeed cache plugin, that plugin has a feature to truncate all the query string parameters from the assets URL but most of the time, it also removes the query string parameter from the Google Maps library URL that is required to validate the API keys, so in order to fix such issue, all you need is to add these lines in the LiteSpeed cache plugin settings.
Once you will add these two lines, it should resolve your problem, or you can contact us through our support.