I can't put the private key in CI/CD variables

I put private key in CI/CD variables and when the ci try to access the variable. This error occurs.

Error: Invalid argument PRIVATE, must be in key=val format
ERROR: Job failed: exit code 1

from what I understand the PRIVATE word is from the first line of private key which looks like this "-----BEGIN PRIVATE KEY-----\n.....

Can someone help? I'm not sure what I did wrong.