How to fill in the tax number of the taxable voucher? Let’s take a look below. 1. Open the electronic tax bureau and click on the combined tax return for property and behavioral taxes. 2. Click on stamp tax source selection. 3. Click to add a new tax source. 4. Fill in the contract number in the taxable voucher number column. 5. Click Save to complete filling in the tax number of the taxable voucher.