Error Undefined class constant 'SQLSRV_ATTR_ENCODING' (no replies)

Here's my system info.
1 - Windows Microsoft Windows 10 Home
Version 10.0.18362 Build 18362, System Type x64-based PC
2 - Version WampServer Version 3.2.0 - 64bit
3 - Apache Version Apache/2.4.41 (Win64)
4 - PHP Version PHP/7.3.12 - Port defined for Apache: 80
5 - MySQL Version - not installed
5a - MariaDB n/a
6 - What color is the WampServer icon:Green
7 - In the file c:\Windows\System32\drivers\etc\hosts, what are the active lines?
#
127.0.0.1 localhost
::1 localhost
If the WampServer icon is green:
8 - Do you have access to localhost (Homepage WampServer) - Yes
8a - If so, is there an error message at the bottom of the page? - No
9 - Do you have access to phpMyAdmin? - Yes
11 - If you use an Antivirus and / or Firewall, please include the names of these: Trend Micro
12 - What is the full path to the installation of WampServer (eg D:\wamp\) - C:\wamp64

EXACT error message:
I’m trying to install DaDaBik – a php form builder using MS sqlserver as my database engine
When I key in [localhost] I get the following error:

( ! ) Error: Undefined class constant 'SQLSRV_ATTR_ENCODING' in C:\wamp64\www\magnal\include\config.php on line 1072

The actual lines in config.php that trigger the error are:
if ($dbms_type === 'sqlserver'){
// MS SQL Server unicode connection encoding
$sqlserver_conn_additional_attributes[PDOSQLSRV_ATTR_ENCODING] = PDOSQLSRV_ENCODING_UTF8;
}
The forum editor is messing up the PDOSQL strings which actually have double colons between PDO and SQLSRV in the original file.
Thanks
Elliot