Test says my Gemini key is not valid. What is wrong?

Almost always the paste caught a space or lost a character. In BookyAI empty the key field, go back to Google AI Studio, press the copy icon next to the key again, paste it into BookyAI, press Save, then Test. A Gemini key usually starts with "AIza" and is 39 characters long. If Google AI Studio says it is not available in your country, the free Gemini key cannot be used there: use OpenRouter instead, which also has free models.