If a such error shows up when Social Login is used:
Check your PHP version and be sure that is at least 5.4+ and also see how it works when you deactivate all the other scripts (plugins and themes).
If a such error shows up when Social Login is used:
wp-content/plugins/indeed-membership-pro/classes/hybrid_auth/hybridauth/vendor/composer/../../hybridauth/Hybrid/thirdparty/OAuth/OAuth.php
Check your PHP version and be sure that is at least 5.4+ and also see how it works when you deactivate all the other scripts (plugins and themes).