After the buyer completes the purchase on the Douyin platform, he can find the "Apply for Invoice" button on the live broadcast page or the order page and fill in the relevant information according to the prompts. The specific steps are as follows:

1. Log in to the Douyin platform and open the order page or the corresponding live broadcast page.

2. Find the "Apply for Invoice" button and click it to enter the invoice application page.

3. Fill in the invoice header, tax number and other relevant information, and select the invoice type.

4. After confirming that the information is correct, click Submit Application.

5. The platform will issue the corresponding invoice to the user within 7 working days.