A customer cannot install an APS application in the POA Customer Control Panel, it says that requirement is not satified. It may be any requirement defined in an APS application APP_META.xml file, e.g. MySQL database as in the example below:
At the same time in the Customer Control Panel it may be seen that corresponding resource is present in a customer subscription, e.g. MySQL 5 databases are present in the subscription in question:
Most likely there are no available units of this resource, i.e. limit of the resource in a subscription is equal to usage. POA not just checks if the required resource is present in a subscription during APS application provisioning, it also checks if there is available unit of the resource.
On the screenshot above it may be seen that customer has limit of 2 MySQL5 databases in their subscription and 2 databases were already created. Wordpress needs to create dedicated MySQL database, however limit for databases has already been reached, which causes 'Requirement not satisfied' message.
A customer has to purchase an additional unit(s) of the required resource or the one in use should be released.
See also the Parallels Knowledgebase article #117971 about the similar problem with not satisfied PHP extensions requirements during an APS application installation.