IOS PEN certificate error
We are trying to add the IOS pen certificate ON Campaign (already managed to add the Android server key without an issue) and have been getting this error:

Mobile Error code:21 - Invalid iOS certificate. Empty certificate key. Could not open a connection with APNS/APNS_SANDBOX server. Error while executing the method 'ChangeMobileApp' of service 'nms:mobileApp'.
Our mobile dev told us he had created IOS certificate many times before without an issue.
Any idea how we can solve this?
Thanks in advance