I'll help you with classifying pension payments in QuickBooks Self-Employed (QBSE), Briony.
In QBSE, you can categorise pension payments as Business Insurance. However, I recommend consulting your accountant for the best category that fits your account or record. He or she can provide you with specific details and analyse your financial information.
To learn more about the different categories you can use for your transaction, you can check out this article: About SA103F Categories.
Aside from pension payments, you can also get more topics and references about managing your other transactions through this link: Help articles, video tutorials, and more.
If you have any other follow-up questions about categorising pension payments in QBSE, let me know by adding a comment below. I'm always here to help. Keep safe always!