Since you are using cPanel, you might want to check if the username prefix is there - generally it will be your cPanel username with an underscore and then your actual username. The same may apply to your database as well. If you are able to login correctly, then your database is working okay.
Replace all instances of ruc_no with gst_no and R.U.C. No: with GSTNo: in your suppliers.php file. Looks like there is something wrong with your FA php files itself. The suppliers table is missing the supp_ref field and the gst_no field is wrongly named ruc_no.
DROP TABLE IF EXISTS `0_suppliers`;
CREATE TABLE IF NOT EXISTS `0_suppliers` (
`supplier_id` int(11) NOT NULL auto_increment,
`supp_name` varchar(60) NOT NULL default '',
`supp_ref` varchar(30) NOT NULL default '',
`address` tinytext NOT NULL,
`supp_address` tinytext NOT NULL,
`gst_no` varchar(25) NOT NULL default '',
`contact` varchar(60) NOT NULL default '',
`supp_account_no` varchar(40) NOT NULL default '',
`website` varchar(100) NOT NULL default '',
`bank_account` varchar(60) NOT NULL default '',
`curr_code` char(3) default NULL,
`payment_terms` int(11) default NULL,
`tax_included` tinyint(1) NOT NULL default '0',
`dimension_id` int(11) default '0',
`dimension2_id` int(11) default '0',
`tax_group_id` int(11) default NULL,
`credit_limit` double NOT NULL default '0',
`purchase_account` varchar(15) NOT NULL default '',
`payable_account` varchar(15) NOT NULL default '',
`payment_discount_account` varchar(15) NOT NULL default '',
`notes` tinytext NOT NULL,
`inactive` tinyint(1) NOT NULL default '0',
PRIMARY KEY (`supplier_id`),
KEY `supp_ref` (`supp_ref`)
) ENGINE=MyISAM;
RUC [General/National Taxpayers Register by its acronym in Spanish] Nr.
Which CoA are you using and from where?