Field 'po_qnty' doesn't have a default value

As others said, this is caused by the STRICT_TRANS_TABLES SQL mode.

To check whether STRICT_TRANS_TABLES mode is enabled:

SHOW VARIABLES LIKE 'sql_mode';

To disable strict mode:

SET GLOBAL sql_mode='';

But the next time MySQL restarts, these settings are lost.

It should be:
[mysqld]
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

instead of
[mysqld]
sql_mode="NO_ENGINE_SUBSTITUTION"

then restart mysqld service.