As there is no idea of subscriptions in the Web Admin and App editions, occasionally a domain will send out subscription expiration notices ~90 days after creation.

The remedy used is to set the expiration date to none, using the following command:

#plesk db "update Limits set value='-1' where limit_name='expiration'"

Prior

root@server:/usr/local/psa/bin# ./domain -i yourdomain.com

General

=============================

Domain name:                            yourdomain.com
Owner's contact name:                   Admin User (admin)
Domain status:                          OK
Creation date:                          Feb 13, 2015
Expiration Date:                       May 7, 2015
Domain administrator:                   No
Disk space limit:                       10.0 GB
Size:                                   764 MB
Total size of backup files in local repository:0 B
Traffic limit:                          100 GB
Traffic:                                11.9 MB/Month

After 

root@server:/usr/local/psa/bin# ./domain -i yourdomain.com

General

=============================

Domain name:                            yourdomain.com
Owner's contact name:                   Admin User (admin)
Domain status:                          OK
Creation date:                          Feb 13, 2015
Expiration date:                        Unlimited
Domain administrator:                   No
Disk space limit:                       10.0 GB
Size:                                   764 MB
Total size of backup files in local repository:0 B
Traffic limit:                          100 GB
Traffic:                                11.9 MB/Month