PHP is not able to input data from Unity to an empty SQL

I have a weird thing happening with my PHP script. Currently, I have an SQL database and a simple PHP script to insert a new entry.

The case is :

if The PHP script is executed directly from chrome, the PHP is able to insert a new entry into SQL(even if the database is empty).

if the SQL database is NOT empty, I can insert a new data entry with the same PHP script from unity (WWW request).

However, when the SQL database IS empty and I try to execute the same PHP script from unity; it isn't able to create a new entry in the SQL database.

have someone experience with this weird issue? please give me some idea on how to fix this problem