To get the PIN:
1. Sign in to your Admin console in admin.google.com.
2. From the left menu click Apps > Google Workspace > Google Voice.
3. In the resulting page click Number porting.
4. At the top, click Port-out info.
5. Click Close when you are done.
Besides the PIN number, they may ask for additional information, in the following sections:
|Bill to||The Business Address specified in the Settings section of your billing account.|
|Invoice date||The date the invoice was generated.|
|Payment terms||The terms specified in your account contract for making payment. Typically net 30.|
|Billing ID||A unique number assigned to the company or individual that the account is registered to. It appears in the Settings section of your billing account.|
|Account ID||The primary domain name associated with your service account.|
|Due date (on the right under total amount due)||The date that the payment is due. The span of time between the period end date and your due date depends on your payment terms with Google.|
|Addresses for payments||The addresses for customers who pay by wire transfer or check.|
|Subscription||The Google product or service that you’re being billed for.|
|Description||The associated cost—for example, usage, commitment renewal, and so on.|
|Interval||The period of time that the costs were incurred.|
|Quantity||The number associated with the subscription—for example, 6 licenses, 1 domain registration annual commitment renewal, and so on.|
|Amount||The actual cost incurred and due.|
Porting out Voice Numbers: https://support.google.com/a/answer/9530249
View invoice details (for reference): https://support.google.com/a/answer/1355897