I checked the rule itself and the event scheduler. Just as a test, I had it running every five minutes. However, when I checked on the lambda's cloudwatch log group, there was nothing. Rule state is enabled. The trigger is there in the lambda. In the cloudwatch metrics, there's actually data, but nothing is logged. It also reports a success so I don't think it's a permissions issue. Also, when I tried to add the rule's ARN to the Configuration>Permissions tab, it reports an error because the ARN contains a forward slash and it allows backward slashes.
I'm using the code from this guide: https://aws.amazon.com/blogs/security/how-to-monitor-expirations-of-imported-certificates-in-aws-certificate-manager-acm/ so I don't think it's the lambda itself. I also just put a print statement in the lambda_handler just to see if anything outputs. Nothing does.
