Renewing your license subscription after it has expired is possible, but renewal discounts may not apply.
Renewal discounts can apply for up to 60 days passed your subscription's expiry date. In such case, any renewed subscription will last one year counting from your last expiry date.

Please also refer to the following articles:

How to renew your subscription
https://www.nomachine.com/AR03D00373

Why renewing your NoMachine Server license is important
https://www.nomachine.com/AR03D00365

Purchasing a subscription from the NoMachine for the Enterprise range
https://www.nomachine.com/AR10K00711

NoMachine EULA
https://www.nomachine.com/licensing