In order to direct extension users to the online store that sells
licenses for this extension, the link to the online store is placed on
the screens of the extension. For an example, see the “License required”
messages in section “Available Licensing Models”.
Resellers or Service providers may choose to manipulate this link
depending on how they wish to sell licenses to their customers (see the
Administrator’s Guide section “Reselling
extensions”
for information). Therefore, it is important know how to correctly
provide and obtain the online store URL that is actual for this specific
Plesk installation.

1. Do not hardcode the specific online store URL into the extension GUI.
2. Use the buy_url property in the meta.xml file
   to provide the online store URL. For example, extensions sold through
   Plesk Online Store have in their meta.xml files the following
   entry: <buy_url>https://go.plesk.com/buy-plesk-ext/</buy_url>
3. Use the appropriate SDK methods to retrieve this URL.

Obtaining License Purchase URL

Use the
pm_Context::getBuyUrl()
method to get the actual online store URL.

Plesk will generate a URL similar to this:
https://go.plesk.com/buy-plesk-ext/example?kn=PLSK.00000001.0000&buyUrlCoupon=happyHacking

Obtaining License Upgrade URL

When implementing Multiple Offers licensing, you will need to provide a
user with directions to where they can upgrade their license, if they
need. Use the
pm_Context::getUpgradeLicenseUrl()
method to obtain the actual URL for upgrading the current extension’s
license.

Plesk will generate a URL similar to this:
https://go.plesk.com/buy-plesk-ext/example?kn=PLSK.00000001.0000&ekn=123456&a=upgrade

The time when to present the user with the invitation to upgrade the
license is up to the developer. Usually, it is done when one or several
of the corresponding resource limits are either depleted or nearing
depletion.