Sorry for late response, the notification from www.ads-software.com went to spam for some reason.
I checked your code and I see that the script is included twice:
<script type='text/javascript' src='https://149442961.v2.pressablecdn.com/wp-content/plugins/get-stripe-customer-portal-lite/modules/js/ajax.js?ver=5.9.3' id='gscp3770ajax.js2430-js'></script>
and
<script type='text/javascript' src='https://149442961.v2.pressablecdn.com/wp-content/plugins/get-stripe-customer-portal-lite/modules/js/ajax.js?ver=5.9.3' id='gscp2755ajax.js5355-js'></script>
I am not sure what makes it happen, maybe some caching plugin or js/css optimizer. While this can be mitigated in the plugin itself it’s unlikely to be the plugin’s issue. I will add a note to fix that in future releases but can’t promise how soon. Try deleting this plugin and re-installing it again. Then if you have some caching/optimizing plugins try deactivating them and see if that solves the problem.