Keep getting key not found when using AWS S3 CopyObject command

Getting the following error when trying to use the copyObject command (AWS S3). I'm using the AWS PHP SDK, and here is the code:

$this->client->copyObject(array(
    'Bucket'     => 'lms-courses',
    'Key'        => 'ideasfile.zip',
    'CopySource' => "lms-courses/lalala.zip",
));

Error executing "CopyObject" on "https://s3-us-west-2.amazonaws.com/lms-courses/ideasfile.zip"; AWS HTTP error: Client error: PUT https://s3-us-west-2.amazonaws.com/lms-courses/ideasfile.zip resulted in a 404 Not Found response: NoSuchKeyThe specified key does not exist.lalala.zipE698888 (truncated...) NoSuchKey (client): The specified key does not exist. - NoSuchKeyThe specified key does not exist.lalala.zipE698888912B810F7DfHtqN5Hls4hGdTGY/pVv36XZPzoM4mJ5fAdhJjEjDufNUArvKCrqN27SjiG06u5hnC8G8yPdzA=

I've been struggling with this error for awhile now. The bucket lms-courses exists, and so does ideasfile.zip. I even manually added that file into the bucket, just to test it out that way - in case that it didn't upload properly or something.

I don't get why it says that the key does not exist, when it clearly does - I am looking at it.