Certificates created by 3rd party tools like OpenSSL may not be properly recognized by the P365 interface governed by Azure AD. Therefore, for the import of the SSL certificates to work follow the below steps.
Import the cert generated by OpenSSL into the MMC | Cert Snap-in-install
Export the cert created by OpenSSL by using the export wizard ensure the following options are selected during export
Export | Export Private Key | Enable and provide a password | select TripleDES-SHA1 | Export to newfilename/path
Retry import into P365. The import will be successful.