A: AI providers like Google Gemini and OpenAI allow you to create API keys. When an app uses such a key, your Google or Openai account gets charged for the AI use on a per token basis.

BYOK is for high volume users that want to use their own keys, control model selection, and produce a large quantity of books.

When you submit a project and you are on tier 3 or 4, you have the option of enabling BYOK. Thsi will discount the project credits by 80% or 90%. Youbooks will then use your keys to do all AI operations needed to complete your project.