After adding extra IPs via WHMCS they are added to SolusVM but not inside the VPS.
The behavior has been submitted as a SolusVM bug #SVM-3346 that will be fixed in future releases.
Once the fix is released, update SolusVM
Until then use the following workaround:
- Deploy a VPS via WHMCS
- Go to SolusVM > Virtual Servers > VPS
- Rush the Re-Configure button