HMRC requires that you keep a record of all your side business income and expenses. HMRC may need to check that you have filled out your tax return correctly, in which case they may ask to see your records.
Uploading your receipts on the Earnr app makes this easy. You can email us at any time and we'll send you a copy of all your transactions and receipts which would (if complete) satisfy HMRC's inquiry.
You don't need to upload receipts or invoices to Earnr in order to submit your tax return. But you do need to keep evidence of those documents somewhere, just in case HMRC ever asks to review your tax return.
You can also add other documents to Earnr for safekeeping... such as proof of postage!