What proof of income for self assessment is needed.

[Mummame2222]

Most of my customers don’t request invoices so I don’t do them, it’s time consuming. Will HMRC expect to see them if they audit me?

What you’ve got to able to prove is that’s you’ve declared all your income so you’d need something to support that in case you ever got an enquiry. It could be something as simple as a list of jobs thst you note down with amounts and tick off when they’ve been paid.

If someone pays you in cash, how are you inputting that transaction into Quickbooks?

When you use sequential invoices, your customers use the invoice number as their payment reference. If you receive cash, then you mark on the statement what invoice number that relates to.
If you keep hold of the cash rather than paying it into the bank (petty cash) then you show on your copy of the invoice where that cash went.
It's about creating the trail. No point trying to be clever (although I don't suspect you of this). If you're declaring £20k profit but living a 50k lifestyle, someone somewhere will dob you in, trust me.
I'd strongly recommend you do invoice for every job, even if the customer doesn't want an invoice, as you need to keep track of your turnover to ensure you don't unknowingly stray into VAT territory. You need to be aware of your last 12 months turnover - not the turnover of your financial year.
Of course you want to spend your working minutes generating income not doing admin, but you also want to sleep well.
Council tax and HMRC - always play the game their way.

I have no idea why my previous post was hidden - I asked about how the OP was inputting cash data into Quickbooks. I'm an accounting professional and was going to offer assistance on the best procedure for accounting for cash transactions in an accounting software package.