If you want to book cash payments on the orderbird MINI, you can do this using a negative amount.
Please keep in mind
Negative amounts are not listed separately in the reports, but are offset against the sales of the cash register day. This means that the report only contains the sum of income and expenditure.
This is how you post a negative amount
Create a product with a negative price (just tap the minus sign for the price and enter the amount). You can then book this as usual.
Or use items with a free price, change it to negative and enter the amount.