How to obtain the CSP ID
Microsoft refers to the term 'CSP ID' in some communications with partners. The correct term should be CSP Subscription ID.
The CSP Subscription ID can be obtained from the CSV usage file sent out together along with the monthly invoices to partners.
Please note that each tenant may have multiple CSP Subscription ID's listed, if Microsoft requests that your provide them a CSP Subscription ID, then only one of them is required.