Help needed: Enfold installation fails on Mac (local install)

Hi there,
I purchased Enfold yesterday, and I wanted to set it up as a local installation on my MacBook Pro (MacOS X High Sierra v10.13.4) to build the website “offline” because the real domain is running with an old web-content which I want to get rid off once the new site is made.
What did I do:
I installed MAMP (Version 4.4.1 -3114), i installed WordPress (4.9.5–de_DE), configured everything. WP is working fine with it’s standard theme, PHP is working (v7.2.1), mySQL is working (v5.6.38), I am connected to the default WP-Site. All fine so far…
So I went to Appearance –> Themes –> Add –> Upload Theme –> put in the correct path to “enfold.zip” –> install now
But then I get the following error: “The link you have followed has expired! Please try again” (German translation: Der Link, dem du gefolgt bist, ist abgelaufen. Bitte versuche es nochmal).

I read in the forum that it is also possible to upload the files with FTP. But unfortunately Apple fu***ed around with this protocol in MacOS X High Sierra… I wasted the whole day in googling and trying various ftp-apps, etc. but I didn’t get it solved.
I am sure that this must have something to do with a local installation on the MacBook Pro, but maybe you guys at Kriesi or someone else here in the forum have an idea for me how to get this working? I would be really happy for some help.
Thanks in advance.
Edit: Oh and I watched *all* the videos, and read forum, and used google… /sigh o_O
/Tom