When trying to create an order for a client in WHMCS the following error occurred:
Unable to get ip id by address 126.96.36.199 from db
where 188.8.131.52 is external IP address and Plesk is using a local one
Additional admin credentials defined in WHMCS Module.
The issue was caused by a bug in WHMCS Module.
WHMCS > Product/Services > Servers > find appropriate server > in the right side click on 'Edit' > in block 'Server Details' please specify 'admin' as user and it is credentials > try to create order for a client.