First, we're assuming your "cash" actually comes from a bank account. That bank account is likely auto-importing into LessAccouting, whereas a cash account cannot be connected. Here's what to do:
Set up a manual cash account:
Go to Settings > Create a financial account
Select Choose this method under the Manual Importing & Data Entry option. Name the account and tell us how much is in it currently
Save your changes.
Tracking the fund transfer:
Whenever you take money out of your bank account, you will need to track that as a funds transfer. We usually manually detect transfers, but only if you are auto-importing from your accounts. In the case of the cash account, you are manually adding data, so we can't detect it. So here's what you do:
Delete the expense from your bank account that is auto-imported
Manually create a funds transfer by clicking "+ Transfer" on the Transactions dashboard. Tell us which account the money came from and went to, the date, and the amount. In your case, it'd be coming from the bank account and entering your cash account
Tracking expense from the cash account:
When you spend money from the cash account, simply manually add expenses by clicking + Expense on the Transactions dashboard for each transaction.