The FTP service is a business feature. Usually you need to order a Business Plan to use it. However, you should be able to try it. In your case, you were able to log in, so the FTP server did not block your account. I guess you used incorrect folder/file path? The easiest way to test it is using a GUI-based FTP client such as FileZilla. Please check if you can access our FTP server using FileZilla. For info about how to use FileZilla, please watch this video:
https://youtu.be/RF1E3sD_bn0