Nginx Proxy Manager Certificate Key is not valid

When adding custom SSL on Nginx Proxy Manager, i get following error.

Upload failed: Certificate Key is not valid (Command failed: openssl ec -in /tmp/15dbf072-4022-aee94-0f88e4fb8d86/tmp -check -noout 2>&1 )

I tried upgrading Nginx Proxy Manager to the latest version with the following commands

cd ~/nginx-proxy-manager/
docker compose down
docker compose pull
docker compose up -d

Even after the upgrade, this error persists.

I checked logs for the docker container, but there were no errors.

docker logs -f nginx-proxy-manager_app_1

To fix this error, I edited the SSL key file.

Find

-----BEGIN PRIVATE KEY-----

Replace with

-----BEGIN RSA PRIVATE KEY-----

Find

-----END PRIVATE KEY-----

Replace with

-----END RSA PRIVATE KEY-----

Now close the SSL upload dialogue and start over the custom SSL upload process. It will work.