Sometimes, a link might look like it doesn't have a key, or it might be a folder link. However, if the URL does not prompt you for a key, the key is likely already embedded in the URL structure or the file is set to public access (rare for MEGA, but possible with the new "MEGA Drop" feature or specific sharing settings).
You must obtain the password directly from the uploader. How MEGA Protects Your Privacy and Data how to open a mega link without decryption key link
If you want, I can: