Thanks for joining in this thread, @Apt7855. I'm here to answer all your questions and to make things clear for you about the importing feature in QuickBooks Online.
You're right, QuickBooks Online only supports Excel CSV (comma-separated values) format. And that's correct, bank transactions can also be imported using that file format.
For more detailed formatting and a step-by-step guide of importing from a CSV file, check out this help article: Import bank transactions using Excel CSV files.
Concerning the Application Programming Interface (API), we have a different dedicated Community site that can provide you with this kind of information. You can check out with our developers by visiting the Intuit Developer Support site, then click the QuickBooks Online tile. Start posting your concern by clicking the Ask a question button.
Should you have other questions, the Community is here to back you up. Stay safe.
