How do I import Apple Numbers files?

I read that all versions after 5.0 can read Apple Numbers files. I have version 6 on Linux, but Numbers files will not import. Please advise

Any error message? There is a filter for Apple Numbers (*.numbers) in File -> Open,thus it should work and if not you should get any message or explain in detail, what isn’t working. May be an anonymized example .numbers file not importing might be also helpful.