If income cannot be attributed to any other type of income, it may fall under "income from other benefits". The law provides examples of other benefits, such as occasional brokerage and the rental of movable items (§ 22 No. 3 EStG).
Income from "other services" is tax-free if it is less than 256 Euro per year. This is not an allowance, but a tax exemption limit. This means: A total profit of 255 Euro is tax-free, but a profit of 256 Euro or more is fully taxable.
Note: If an employee receives money from their employer for attaching a number plate with the employer's logo to their private car, this is considered taxable income. The employer's view that this payment is not income but tax-free other income up to 255.99 Euro per year was rejected by the Federal Fiscal Court (BFH decision of 21.6.2022, VI R 20/20).
