.pfx S/MIME certificate generated with openssl - password is not recognised when imported on an iPhone

I have recently obtained an S/MIME certificate from a CA to use with Thunderbird on a Linux system. I used the following command in CLI : openssl pkcs12 -export -in certificate.crt -inkey private_key.pem -certfile cert_CA.crt -out my-cert.pfx I then installed my-cert.pfx in Thunderbird and this works just fine. I proceeded to also import the same .pfx file onto my iPhone bu this results in an error when asked for certificate password. Entering the established certificate password doesn't work as per instructions and it looks like it's not recognised, even though I am sure I have used the correct password ?!? I am not sure but I suspect that by default the openssl command may have encrypted the output .pfx certificate file with a different encryption to that which iOS expects by default, and so the same certificate password is not recognised correctly. Any suggestions as to what may be the problem and how to generate a .pfx file using openssl in CLI so that iOS will accept the set certificate password ? I had used the Windows Certificate Manager Tool to export my private key and this required setting a certificate password (no other option was available). Thanks in advance for any suggestions on how to correctly generate and import the .pfx certificate file to work on my iOS devices...