There is only one version of the Juicebox-Pro v1.5.1 zip file (named 'juicebox_pro_1.5.1.zip').
When extracted, you should have a folder named 'juicebox_pro_1.5.1'.
Directly inside this folder you should see the following contents:
Inside the 'adobe-lightroom-plugin' folder is the 'juicebox_pro.lrwebengine' folder/package that you would drag and drop onto your Lightroom desktop shortcut to install the 'Juicebox Plugin for Lightroom' in Windows.
As I mentioned, there is only one version of the Juicebox-Pro v1.5.1 zip file so your own zip file should contain the contents above.
If not, then perhaps your download is somehow corrupt or incomplete.
Please check the integrity of your 'juicebox_pro_1.5.1.zip' file. It should have the following properties:
Name: juicebox_pro_1.5.1.zip
Filesize: 1,912,372 bytes
MD5: 684b9d42be40906ac775aecfbb8631d8
SHA1: 872bcd0b62ef9841eab672e6a12f431919a4d969
You can check the MD5 and SHA1 hashes of files with a free program such as HashCalc.
If your own 'juicebox_pro_1.5.1.zip' file does not have the properties above, then please try re-downloading the Juicebox-Pro v1.5.1 zip file with the link from your purchase email.
I hope this helps.
Please let me know how you get on and if I can be of any further assistance.
Thank you.