Summary
If you don't have an SA302, skip the document upload step and continue your verification using your other available sources. Your verifier will review what you've submitted and follow up if they need anything further.
Why you might not have an SA302
You're employed through PAYE and don't file a Self Assessment return
You haven't filed Self Assessment for the tax year your verifier is asking about
Your accountant filed on your behalf and you haven't downloaded the SA302 yourself
You've recently moved to the UK and haven't yet filed a return
What to do
Skip the document upload step and continue. Connect any other sources that are available to you - HMRC and your bank account can both be used to verify employment and income. Once you've connected what you can, submit your verification.
Your verifier will review the result and should contact you if they need anything else - They may ask for alternative evidence outside of Konfir.