Install activation crashes site

That is quite a severe error. The first thing to do is access the site via FTP and delete the plugin, this will at least give you access to your site.

I’m not hearing reports of this happening to other users, so I can only assume it is due to a conflict with another plugin you have installed. If you have another POS plugin installed it’s possible that we have inadvertently given some functions the same name – this would cause a fatal error.

If you do have another POS plugin installed you should deactivate that before installing WooCommerce POS.