The original creator of the below code is mabdelaziz77 and we want to thank him for creating and above all sharing this code with the world. The code is efficient and quick to understand and it helped us a lot and we are sure it will help a lot of other people as well. So thank you very much!

This is a custom Form Field to help Joomla! extension developers to implement the Joomla Update System and meet the new JED requirement for PAID extensions.

This field is developed to be used with RD Subscriptions packages, although it can be customized to work with other subscriptions and release/download managers.

language/en-GB/en-GB.mod_yourextension.ini (modify each language)
models/fields/downloadid.php (needs to be added)
mod_yourextension.xml 

First of all, download the downloadid.php file and add it in a proper folder inside your extension package we recommend models/fields, so the the relative path should be mod_yourextension/models/fields/downloadid.php

Now, the Download ID field is ready to be used as any other standard form field within your installation xml file.

This is an example of parts of a module installation file, let's say mod_yourextension.xml So the workorder is: Add files, fieldset and then the updateserver.

<files>
  <folder>models</folder>
</files>

<updateservers>
  <server type="extension" priority="1" name="Your Extension"><![CDATA[http://domain.extension/index.php?option=com_rdsubs&view=updater&format=xml&cat=#&element=mod_yourextension&type=module]]></server>
</updateservers>
<!-- Where # is the catagory number. Use the RD Subscription build in Menu item: Joomla XML Feed to generate the correct links. -->

<config>
  <fields name="params">
    <fieldset name="subscription" addfieldpath="/modules/mod_yourextension/models/fields">
      <field
	name="dlid"
	type="downloadid"
	label="MOD_YOUREXTENSION_-AUTOUPDATESUBSCRIPTIONTOKEN-_LABEL"
	description="MOD_YOUREXTENSION_-AUTOUPDATESUBSCRIPTIONTOKEN-_DESC"
	default=""
	extension="Your Extension"
	key="key="
	/>
    </fieldset>
  </fields>
</config>

Important

The Download ID field has two important additional attributes, extension and key where:

extension: must be the same as the name attribute of <server>, this is very important to set the update the correct record in the update_sites table.

key: has a default value of "key=" which is used with RD Subscriptions combination, of course you can give it any other value if needed with any other subs and release managers.

Note:

You can use the Download ID field as it is, without any guarantees.