You can just tag things to “Something else not on the list” and post it directly to a nominal account (like ‘General Sales’, which is basically what invoices use by default. However, I think from an accounting or tax point of view, this wouldn’t be recommended seems you wouldn’t be able to match things up (e.g. Income from Customer A; Purchases from Supplier B) - at least, not so easily.
Maybe someone with more accounting knowledge would be able to clear that up for you.
As per @Parker1090 suggestion you can just upload a bank statement and tag everything directly to nominal accounts using Something else not on this list. HMRC would require you to evidence all sales and purchases so this is fine as long as you have another way to show this. This method won’t be suitable if you are VAT registered as the invoices will be required to itemise the VAT.