Yes, Google has changed its "Google Maps APIs Standard Plan" since june 2016.
(https://googlegeodevelopers.blogspot.nl/2016/06/building-for-scale-updates-to-google.html)
In the meantime you could try the following:
In ...zp-core/zp-extensions/GoogleMap.php
change line 140 from
`<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?v=3.exp<?php echo $loc; ?>"></script>`
to
`<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?key=YOUR-KEY-HERE"<?php echo $loc; ?>"></script>`