Do you use MySQL 5.7?
There is a bug in mpos, There is a workaround

s MySQL 5.7+ Supported?
Yes and no. When they wrote MPOS the queries were not the best, with the newest version a new restriction was added that will cause some queries using GROUP BY to fail. They were fuzzy at best and worked all the time, but with the new version MySQL rejects them. Since nobody has time to go through MPOS and fix all queries affected, here a quick workaround for your database server:

mysql> set global sql_mode=’STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION’;
This setting is lost so either make it permanent via you my.cnf or re-run the query to reactivate this option.

MySQL update when it came to my server. I ran this and my cron and payout woes went away:
mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';

OS
Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic
MySQL
mysql Ver 14.14 Distrib 5.7.23, for Linux (x86_64) using EditLine wrapper

I can also confirm that MYSQL solution works with Ubuntu Server 18.04.

In /etc/mysql/mysql.conf.d/mysqld.cnf anywhere under [mysqld] add:

sql_mode = STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

Save file, restart mysql service and everything works.