DeepL API
DeepL offers free API access that allows you to translate up to 500,000 characters per month for free. If you need more than that, you can purchase a DeepL API Pro subscription and it costs $5.49 / month + Usage based price
Complete the subscription process.
After you have subscribed, go to your Account https://www.deepl.com/account/summary and under the tab with the same name you will find your API key.
Copy the API key, then in the VNTranslator go to Service Settings and enter your key.