Quick Summary of this page

If a user can pay real money to get access to the plugin or any of its features, or to enhance their experience with the plugin in any way, that’s considered commercial use. Even if you provide other free ways to get access. Even if you are not the direct beneficiary of the payments.
Otherwise, the plugin is considered non-commercial.
Asking for donations, requiring users to purchase and subscribe to the game itself, is allowed for non-commercial plugins.

Commercial Use - Detailed

By default, all commissioned plugins come with non-commercial use only permission, unless you specifically request commercial use. This means:

You cannot sell the plugin or access to it for real-world money, directly or indirectly;
You cannot restrict access to individual plugin features behind a paywall, and you cannot offer upgrades to individual plugin features for real-world money, directly or indirectly;
If a plugin is used to create a new, unique product, the restrictions listed on this page apply to that product as well;
Forks of the plugin or other products that contain the plugin’s source code, or the plugin itself, are also subject to the restrictions listed on this page.

Exceptions

Donations. You may place your own donation links within the plugin or it’s description if you choose to distribute it yourself. This is not considered commercial use.
Game purchase and subscription. You can require users to own a license for the game the plugin is intended for, as well as maintain their own subscription - this is not considered commercial use. For example, you can require users to be in your Free Company in order to use the plugin, which implies the need to pay for a subscription.
Purchase or subscribe to third-party cloud services. For example, if a plugin requires a paid translation engine or paid file hosting, you can require purchase or subscription to that service and maintain non-commercial status, as long as you are not the owner of or affiliated with that service.

In-game Currency

You may charge in-game currency for any of the above if there is no legitimate way to purchase such in-game currency with real-world money. You may not accept in-game currency purchased with real-world money in a transaction that violates the game’s Terms of Service, and you may not encourage users to engage in RMT.

Plugins that are not commercial in themselves, but are primarily designed to enhance or extend other plugins that are commercial, are also considered commercial.

If a plugin contains a client-side part and a server-side part, even if the server-side part is open source and could theoretically be hosted by anyone for free, if the default server that is either preconfigured in the plugin or advertised in places where the plugin is distributed has paid access or paid features, the entire plugin is considered commercial.

Requesting a commercial use

If you want to use the plugin for commercial purposes, it is possible if you accept a commercial agreement. The following options are available:

The standard commercial agreement is available to anyone for +500% (five hundred percent) of the cost of the plugin. This agreement allows you to use the plugin for all kinds of commercial purposes indefinitely without any restrictions. All future upgrades and updates will also include a +500% surcharge, and there will be no free update period (bug fixes are still free, though).
Individual agreements may be possible, depending on the plugin itself and how exactly you plan to use it. Usually they will involve a cut of the sales (if a reasonable way to track such sales can be established) or a fixed monthly payment. An individual agreement is likely to be more restrictive than a standard agreement, but may also entitle you to free updates and upgrades, and will usually cost you much less.

Conversion from non-commercial to commercial plugin

You don’t have to pay commercial fees right away. Any plugin can be developed as non-commercial and converted to commercial at any time. To convert a non-commercial plugin to commercial, you can

Either pay +500% surcharge on previous fees for both initial development and upgrades (update fees are not subject to this surcharge), accepting the standard commercial agreement, with it’s permissions and restrictions;
Or request an individual agreement.

Conversion from commercial to non-commercial plugin

You can convert a commercial plugin to a non-commercial plugin at any time. This process requires you to publish the plugin and it’s source code under one of the open source licenses. To do this, you should do the following:

Remove the plugin from all shop pages. If the plugin has been used to create other products, those products need to be removed from their stores as well.
In all places where the plugin was promoted, place an announcement that the plugin is now free and place a link to the public download. If the plugin was used to create other products, this action should be taken for those products as well.
Publish the source code on GitHub, GitLab, or elsewhere, and license it under any open source license of your choice. You can also ask NightmareXIV to do this (this service is free).
Notify NightmareXIV via the Discord server or any other previously established communication method.

From the moment your plugin has been converted to non-commercial, you will not have to pay any additional fees for updates and upgrades. In addition, if you are eligible for a free update period, it will be reinstated immediately. Previously paid fees will not be refunded.

Conversion from commercial to non-commercial and then back to commercial plugin

You can convert back and forth as much as you want, no restrictions.

If you convert to a standard commercial agreement, you will only have to pay surcharges for previous fees for which you have never paid the surcharge before.
Please note that your individual agreement expires as soon as you convert the plugin to non-commercial. A new individual agreement must be made and it’s terms may change.

Conversion between Standard and Individual agreements

You can always request an individual agreement, even if you have already paid for a standard agreement. Conversions from individual to standard agreement are only possible by converting the plugin to non-commercial and back to commercial.

Unauthorized commercial use

Commercial use of the plugin without a commercial agreement will have the following consequences:

You will no longer receive any support from NightmareXIV for plugins you have commissioned, including update and upgrade requests;
The plugin and it’s source code will be released under an open source license.

Plugins commissioned before these terms were effective

If you commissioned a plugin before these terms became effective, you may use it commercially without a commercial agreement. However, if you request an update or upgrade for such a commercially used plugin, I may add a +500% surcharge according to the standard commercial agreement. It’s recommended to request an individual agreement for such plugins.

Commercial use via third party

It is considered commercial use if a user can pay to get it, you do not necessarily have to receive that money. For example, giving Discord Nitro Boosters or Twitch subscribers access to the plugin is considered commercial use. Additionally, sales via third party person are considered commercial use as well. If you want to keep the plugin private and non-commercial, you should take reasonable measures to ensure that a user can not resell their copy of the plugin easily.