If you see a purple exclamation mark, the toolkit is suggesting a match between an invoice and a payment you have received. Just click on the symbol, and in the sidebar, you can confirm the suggested match. Confirming a match will attach the corresponding invoice to that transaction and automatically add any VAT details from that invoice onto the transaction. This VAT will now feed through into the VAT estimation tool.
The red symbols mean that you’re missing some information – either VAT (if you’re VAT registered), a business category or evidence of that transaction in the form of a receipt or invoice. Just click on that transaction and complete the missing information.