NoMachine licenses are product-specific. This means that the server package you install must match the product covered by your subscription.

For example, a NoMachine Workstation license can only be used with NoMachine Workstation, while a Personal Edition license can only activate NoMachine Personal Edition. Licenses cannot be used to activate a different NoMachine product.

If you attempt to install a different NoMachine product without first uninstalling the existing one, the installation will be blocked with a message similar to:

Two different NoMachine packages can't be installed at the same time on the same host. Be sure you uninstall [product name] before installing a different NoMachine products.

Or in the logs, you might see:
NX> 630 ERROR: The installed server type [product acronym] is not suitable for the subscription type [product acronym] .
NX> 630 ERROR: Please uninstall the server and install the appropriate product or
NX> 630 ERROR: contact NoMachine to acquire a different subscription.

To solve it, uninstall the current package, install the package that fits your license and install the license.

Some remarks

1) On Linux, you can check which package is installed in the following way.
RPM:
rpm -qa | grep nomachine

DEB:
dpkg -l | grep nomachine

2) With version 9, we introduced online license validation.

All product editions from v9 onwards are validated using the NoMachine licensing server.

On-premise licenses are still available for those customers with air-gapped networks.To find out how this works in detail, see: https://kb.nomachine.com/AR10U01206

4) The new major version 10 introduces a new product, the Personal Edition (with acronym PE), while the free version of the server (with acronym S) has been discontinued.

It is not possible to upgrade a free server installation, or any other server installed, with the Personal Edition because they are different products (as outlined in point 1).

5) Client and Server Version Compatibility

NoMachine clients and servers running versions 8, 9 and 10 can connect to each other regardless of their version combination. For example, a version 8 client can connect to a version 10 server, and vice versa.

The only known exception concerns server versions up to 8.19, which have compatibility issues with version 10 clients.

We recommend using the latest available release of each branch version.

Known Issue on macOS

In NoMachine v10.0.57, package validation on macOS may not properly prevent this upgrade scenario. As a result, users who upgrade from the free version to v10 may encounter an error such as:

For older NoMachine versions

Updating Workstation or Small Business Server installations from v7 to v8 is an out-of-the-box process. There are some exceptions which require a new license and these are detailed here: https://kb.nomachine.com/AR12S01147

What you should do is:

1) Verify that the installed server software matches the license you own. If not, uninstall it and install the appropriate package.

To check which NoMachine RPM package is installed:

rpm -qa | grep nomachine

To check which NoMachine DEB package is installed:

dpkg -l | grep nomachine

2) Upgrade server installation v7 to v8

Installing version 8 from scratch will be necessary if you're using two v7 servers in failover cluster or if you want to adopt any of the new cloud server products (see https://kb.nomachine.com/AR12S01147). In those cases obtaining a new v8 license key is also required. Please contact sales to request new licenses.

For all other products in the Enterprise suite, you can continue to use your license v7 in a v8 installation, just be sure to have the appropriate package installed. To make it easier to find which server package to install, you can download it from your Customer Area (https://www.nomachine.com/customer-details) where only that server type matching your license is listed.

Some related articles:

How to upgrade from Enterprise Terminal Server v7 with failover cluster to Enterprise Terminal Server Cluster v8
https://kb.nomachine.com/AR11T01180

How to migrate NoMachine 7 configurations to a new machine
https://kb.nomachine.com/AR02T01153