CodeIgniter on AWS LightSail

Hi,

New to CodeIngniter ...

I have an AWS LightSail instance with a MySQL database created.The database is set to be publicly available and I can connect to it from an external client.

I have CodeIgniter framework installed on the instance and a pre existing website copied in that worked OK on a different host. I have database.php configured to connect, however I get :-

A Database Error Occurred
Unable to connect to your database server using the provided settings.
Filename: core/Loader.php
Line Number: 357


If I manually connect at the bottom of database.php using the same CodeIgniter configuration I can connect successfully.

Any pointers?

Many thanks,

Mark.