Creating and installing new v3 Ideal certificates for OsCommerce webshop

We need a specialist that is well known with OsCommerce and IDEAL v3 payments We need to create a new set of files for a new IDEAL certificate for our OsCommerce webshop and install them on the webserver for the OsCommerce webshop and upload the certificate to the secure IDEAL dashboard at the ING bank. We already tried this ourselves and downloaded OpenSSL software to create the neccesary files, created them and uploaded them but maybe we used the wrong location in the custom built OsCommerce webshop or maybe we did something else wrong, I don't know. The OsCommerce webshop currently won't proceed to the IDEAL checkout page since the old certificate expired on September 30th 2018.