You can troubleshoot this sort of configuration problem by first enabling WordPress diagnostics.
You will need file access to your site to do this (e.g. ftp).
From the root folder of your site, edit the wp-config.php file to enable logging:

define(‘WP_DEBUG’, true);
define(‘WP_DEBUG_LOG’, true);
define(‘WP_DEBUG_DISPLAY’, false);

Then run through the pfx import process again.
You should now have a debug.log file in your site’s wp-content folder.

Checking in here, if you see errors such as:
RapID: OpenSSL Err: error:02001002:system library:fopen:No such file or directory
then this indicates that your OpenSSL installation is not configured correctly.
This is a common problem with Azure Web-App deployments, where the openssl.cnf configuration file is located in an inaccessible folder.

To work round it, you can copy your actual openssl.cnf file into the ‘certs’ folder within the RapID-SL plugin folder.

In Azure, the openssl.cnf file is likely to be here:

Copy it into the certs folder and try importing the pfx file again.

If you cannot locate your actual openssl.cnf file, there is a sample provided in the certs folder, called sample-openssl.cnf.
Just rename this to openssl.cnf and try again.