Warning: Undefined variable $conn in C:\inetpub\vhosts\tegadistribuidora.com\httpdocs\blog\header.php on line 21

Fatal error: Uncaught TypeError: sqlsrv_query(): Argument #1 ($conn) must be of type resource, null given in C:\inetpub\vhosts\tegadistribuidora.com\httpdocs\blog\header.php:21 Stack trace: #0 C:\inetpub\vhosts\tegadistribuidora.com\httpdocs\blog\header.php(21): sqlsrv_query() #1 C:\inetpub\vhosts\tegadistribuidora.com\httpdocs\blog\articulo.php(24): include('...') #2 {main} thrown in C:\inetpub\vhosts\tegadistribuidora.com\httpdocs\blog\header.php on line 21