Disk size for SolusVM KVM VPS is not being upgraded if it is made from WHMCS

Symptoms 

Disk size for SolusVM KVM VPS is not being upgraded if it is made from WHMCS

Cause

 Allow HDD upgrades (KVM/Xen HVM) option not enabled in SolusVM API access

Resolution

1. Access SolusVM web interface
2. Browse to Dashboard > Configuration > API Access page and click on edit icon against API ID/KEY pair used for WHMCS integration
3. Enable Allow HDD upgrades (KVM/Xen HVM) option and click on Update API User to save changes
   
4. Try to upgrade VPS resources once again and do not forget reboot VPS to apply changes