With the release of Easy!Appointments v1.3.2 the minimum MySQL version requirement was changed to v5.7. The reason under this change is that upcoming Easy!Appointments releases will take advantage of newer MySQL features and allow developers handle data more easily.
Moreover MySQL 5.5 has already reached its end of life and users are advised to use a newer version. More information on upgrading to a newer version can be found in the official MySQL site at https://dev.mysql.com/doc/refman/8.0/en/upgrading.html.
Moving to MySQL v8.0 users will find plenty of new features such as MySQL Document Store, Transactional Data Dictionary, SQL Roles, Default to utf8mb4, Common Table Expressions, Window Functions and much more.