Hello there, @ehong33.
Thanks for asking us about the vendor's Bill Due notification and alert in QuickBooks Online. At the moment, this feature is only available for invoices.
However, if your vendors are also using QuickBooks, you can ask them to have this feature set up on their end so you'll receive an invoice reminder automatically. Otherwise, your workaround which is to pull up your Google calendar and manually enter alerts separately would be the best option.
I can see how this feature is essential for you in your business. I'll do my best to keep up with your request by personally let our Development team know your ideas. Please note that all of our suggested plans are subject to further study. Hence, we'll have to wait until this feature be added in future updates.
In the meantime, you can submit feedback yourself by going to the gear icon and selecting Feedback.
You also might be interested to learn about sending invoice reminders automatically or manually in QuickBooks Online for your customers in the future.
Feel free to comment below if you have any other questions. Wishing you continued business success.
