Welcome to the Community space, @Handlez.
Allow me to help you and share some insights about managing your invoices in QuickBooks Self-Employed (QBSE).
In regards to this, it all depends on you either you want to attach those invoices to your business transactions or not. If you’re unsure of this, I recommend consulting with an accountant for the best advice and action to take.
Also, the transaction page and invoice page are not connected. Thus, assigning income transactions to an invoice is not available.
To learn more about how QBSE works, check out this link for your reference: QuickBooks Self-Employed Overview.
Let me know if there’s anything else I can help you in managing your invoices. I’d be more than happy to work with you again. Take care and keep safe!