Hi @mclim
Could you please show the error message you received in the Get items in detail?
Based on your description, I have made a simple test for your reference.
1. I have a Date and time column with the date showing here:

Here is the flow:

After running the flow, it got the result here:

But when I use the wrong internal column name in SharePoint list, I got the error message "BadRequest.":

So I guess the possible reason that you get the error may be the wrong internal column name for your Open Date column used in the filter query.
Please check the correct internal column name by going to your SharePoint list > Settings >List Settings > Choosing the Open Date column, and the correct name format is showed in the last part of the URL:

Hope it helps.
Best regards,
Sylvia