You can export subscription invoice data for tax purposes by following these steps:
1. On your publication's Settings page, click on Payments in the left navigation bar.
2. Under "Subscription invoice report", select "Request a new report".
3. From here, you can request a report of all invoices created within a time period of your choosing. Once you’ve selected a start and end date, click “Request report”.
4. A .csv file containing your invoice data will be generated which you can download. Once the report is ready, you'll be notified by email. Alternatively, you can view any requested exports or reports at this link:
https://your.substack.com/publish/document_exports
5. In the report, you can a a breakdown of fees, currency, and the type of subscription plan for each subscriber.
For more information on filing taxes for payments you've received from subscriptions, check out this article here.