I've seen this post: Genymotion can't install gapps But here it says that upgrading to version 2.12.1 will solve the problem, but I'm using version 3.1.2 I just downloaded. What should I do?
This post is outdated and there has been problems with sourceforge that broke compatibility with Genymotion OpenGApps widget. Until a fix is released, you need to install the Open GApps manually. See https://support.genymotion.com/hc/en-us/articles/360015897698-Installing-OpenGApps-fail-with-error-Open-GApps-archive-is-corrupted-