From the Knowledgebase

If I buy a license, can I use the product forever?

Yes, the license allows you to use the product indefinitely on your WordPress site. The fee also entitles you to support and updates for 12 months from the date of purchase.

After 12 months, you are free to continue to use the software, but if you require support or updates you would need to buy a new license at that point.

As an incentive to renew annually, we will offer a 50% reduced renewal rate for customers who renew their license before their previous license expires.

When you install the premium product and enter your license key, it will tell you when your support/updates license expires, but of course you will still be welcome to use the product even with an expired support/updates license.

We believe this situation is better than a one-time purchase since you will receive updates beyond the purchase date – at least for a year – and it offers a sustainable position for support and continued product development in the future. A one-off purchase could easily leave you exposed and in need of a new solution a few months down the line.