Error establishing database connection – PHP 7 and subdirectory install issue

Hi,
the site was just moved to a new host, old host was running a version of PHP 5.
The new host is running PHP 7.3

The wordpress install is in a subdirectory “redesign2019”

Before the move, everything fine but after get the error establishing database connection.

I have ensured that the database user, pass and name are correct.

in the index.php file in the root I have this that previously worked on the old server:

require( dirname( __FILE__ ) . ‘/redesign2019/wp-blog-header.php’ );

but now gives the error.

if I change to
require( dirname( __FILE__ ) . ‘redesign2019/wp-blog-header.php’ );

or

require( dirname( __FILE__ ) . ‘../redesign2019/wp-blog-header.php’ );

I get the white screen of death.
I’m just guessing it has something to do with the PHP version. Any help would be awesome, thanks in advance!