How to generate the p12 file for my phonegap build?

My company made a developer certificate on the Apple Developer platform. At this point I need to link a key file to my iOS build in Phonegap.

I'm trying to generate this key file where I need the .p12 file and the provisioning profile file. I've got myself the provisioning profile file, but I can't seem to generate the .p12 file.

I'm using Openssl to generate my files and I tried this command to generate the last file:

openssl pkcs12 -export -inkey ios.key -in ios_development.pem -out ios_development.p12
Enter pass phrase for ios.key: *********
No certificate matches private key

What exactly am I doing wrong here? Can I find the private key on the developer.apple.com website?

UPDATE: here are the steps I'm performing to get to this problem:

1. Generate private key: openssl genrsa -des3 -out ios.key 2048 and enter a password pass123
2. Generate CSR file: openssl req -new -key ios.key -out ios.csr -subj "/[email protected], CN=company, C=BE" and enter the password from the private key pass123
3. Go to your Apple Developer iOS Provisioning Portal and download the development certificate .cer file
4. Convert the certificate to a PEM file: openssl x509 -in ios_development.cer -inform DER -out ios_development.pem -outform PEM
5. Generate the P12 file using the private key (ios.key) and the iOS development certificate (ios_development.pem): openssl pkcs12 -export -inkey ios.key -in ios_development.pem -out ios_development.p12 and enter the password from the private key pass123
6. Error message: No certificate matches private key