PHP 7 is supported for Blesta 4.0.0 and higher.
Every effort is made to stay within the below requirements for the extensions that ship with Blesta. Certain extensions (plugins, modules, and gateways) that ship with Blesta, or which are available through the Marketplace however, may have their own unique requirements. In many cases, recommended requirements include PHP extensions that make additional features available, or improve the performance of certain features.
MySQL changed the default behavior in version 5.7.5 to enable "only_full_group_by". If you are using a version newer than that, or if you had changed your MySQL configuration file to enable "only_full_group_by", you will need to remove it. You should update your MySQL configuration file to disable "sql_mode", i.e., don't have it set to "only_full_group_by". You can run the following query to determine what the sql_mode is: SELECT @@GLOBAL.sql_mode, @@SESSION.sql_mode;