WooCommerce Serial Numbers PRO requires the free version to be installed and activated. Follow the steps below to properly activate WooCommerce Serial Numbers PRO.
NOTE: You must have WooCommerce installed and activated as WooCommerce Serial Numbers works on top of WooCommerce. The minimum required MySQL version is 5.6.
First of all, go to your admin dashboard. Hover over to Plugins and click on Add New.

Search for WooCommerce Serial Numbers and from the search result click on Install.

Once installed click on Activate.

You can also download WooCommerce Serial Numbers from this link and upload it. First of all, click on Upload Plugin, a new option will appear. Now click on Choose File to upload the zip file that you have downloaded to your computer.

After the installation is complete, activate the plugin by clicking on Activate Plugin.

Steps for the premium version:
Go to my account section on PluginEver. You will find a Downloads tab. Click on it and there you will find your desired files to download. Click on the plugin file to download the premium version.

Once the download is complete, upload the plugin and install it by clicking on Install Now.

Activate the premium version after installation by clicking on Activate Plugin.

You will find a WARNING with an option to enter your license and activate it at the top of your plugins page. Click on Enter your license key it will take you to the proper place.

Now go to My Account section. Click on the License Key tab. Here you will find the license key.

When you click on Enter your license key, a field will appear immediately below the plugins. This field asks for putting the license key for your premium purchased product. Once the license key is set, your premium plugin is activated and you are all set to go!
