Symptoms

Application cannot be installed with following error:

Error: Unable to install the app because its installation requirements are not met. Contact your hosting provider to resolve this problem.
Requirements
PHP extension 
The 'IonCube' extension was not found.

Cause

APS package defines incorrect requirement for PHP extension : IonCube instead of ionCube Loader .

Resolution

Contact APS package vendor (link to vendor's site is available in application description in Plesk interface) and advise to update package with proper definition.

Workaround

Find application's APP-META.xml file:

mysql> select * from aps_package\\G;
*************************** 1. row ***************************
                id: 1
registry_object_id: 1
         series_id: 1
  master_series_id: NULL
              name: SupportPRO SupportDesk
           version: 3.0
       archive_uri: /usr/local/psa/var/apspackages/d67afc43-d760-4104-96cd-a952c1e5c1d2.zip
      metafile_uri: /usr/local/psa/var/apspackages/d67afc43-d760-4104-96cd-a952c1e5c1d2/APP-META.xml
        source_uri: NULL

Open it in text editor and replace line

<php:extension>IonCube</php:extension>

with

<php:extension>ionCube Loader</php:extension>

Save file and install application.