For ChatGPT, check the account and purchase channel
In the right account, open Settings → Billing. The past-invoice help also describes Settings → Account → Payment → Manage, followed by Invoice History in the billing portal. Use the route available in your interface and download the document for the period you need.
Current help on past invoices →
An empty history may mean you are signed into another account. It can also be related to a purchase through Apple or Google: look for those subscription documents in the relevant app store purchase history. Using ChatGPT on your phone does not itself tell you how you paid for the subscription.
ChatGPT Business: the workspace owner gets the invoice
For ChatGPT Business, look in the settings of the specific workspace, under Billing and Invoices. OpenAI says workspace owners can view invoices. Ask the owner for the particular period; you do not need to take over their role.
Source for this section: OpenAI explains the separate billing systems
When a document is missing
Check the account, workspace and purchase channel. If billing is inaccessible, ask support to locate the document and provide your email, workspace name or ID, period and any known previous invoice number. You do not need to share conversations or your password.
Source for this section: Current help on past invoices