Welcome to Microsoft Q&A forum.
I understand you're building a Power Automate flow to send email notifications for expired dates in a SharePoint list, but it's failing with a 'Bad Request' error. This is happening even though you've already confirmed the Filter Query uses the correct internal column name from SharePoint.
According to its description, it looks like you are having a problem with the Microsoft Power Automate flow. If my understanding is correct, as our category focuses on Office 365 products, the problem you encountered is related to Microsoft Flow, to ensure that you get professional help and avoid incorrect information from our side, we suggest you post on the Microsoft Power Automate Community for expert assistance. The best place to get assistance is the Microsoft Power Platform Community Forum Thread.
The community forum is actively monitored by Power Automate experts and dedicated users who are best equipped to help you diagnose and resolve this specific 'Bad Request' error.
This forum is dedicated to Power Automate and is supported by a knowledgeable community, including Microsoft experts and partners. By posting there, you'll have access to more specialized resources and insights, which can help resolve your issue more effectively.
I hope this information is helpful and appreciate your understanding.
Should you have any further questions, please feel free to reach out.