After activating the Woocommerce Custom Product Addons plugin, you need to enter the License Key. The license key can be copied from the purchase confirmation page.
The screenshot below shows where the license key exists.
After copying, go to Product Addon >> Plugin License
Paste the License Key in the preferred text box and click on the Activate button.
In the refreshed window, you can see the plugin is Activated
To have a look at the activation status and active URL, navigate to Product Addons >> Settings >> License Activation
Once you have downloaded, installed, and activated the plugin is ready to be used
And you can start building your own custom product form.