Your certificate should be inside a .ZIP archive and have the name like www_your_domain_com.crt (= Certificate *.crt) as well as a My_CA_Bundle.ca-bundle.
The ca-bundle file is the one that needs to be copied into the field CA-Certificate. Your private-key (.key) has been created together with your .CSR, that you have been using for requesting the certificate. We do not store a copy of your private .key, please use the previously created one.