Can't upload certificate to Apple for renewal

I am unable to renew the push certificate for my Mac running OS 11.2.1. I tried a couple of months ago and gave up. My certificate expires in 14 days, and there doesn’t seem to be anything I can do about it. After downloading the certificate from Prey, I try to upload it to Apple, but I get the following error message…

Invalid Certificate Signing Request
The Certificate Signing Request you entered appears to be invalid. Make sure that request file uploaded is in the correct format and not empty.