Multisite Error Establishing Database Connection

I have created a multisite in a sub directory /wp/ and I’m getting a database connection error message. I have copied the index.php and .htaccess files to the root directory and I think they are correct but not having any luck. Can’t get into wp-admin only cpanel and ftp access. First time I’ve created a multisite so bound to be something dumb I’ve done. Also checked that the db was okay via phpadmin. Now officially out of my depth, way out. Any assistance gratefully accepted.