Form Selection Comparison "Compare Not Allowed with this data type"

[mr_g-ski]

I am trying to create a "simple" application for the high school where I work. This is my first time using PowerApps and I love it, but I can't get it to work correctly.

Students will be able to make a few selections on dropdowns (accordingly to their schedule) and then generate an email to their parents with list of links. I created form dropdowns from an excel database but it doesn't allow for comparisons with the data (string?) I am able to generate a preformatted email but I need help getting a form picker that reduces the options based on the previous selection. For reference, consider this tool: https://www.amazon.com/gp/part-finder

Or the screenshot below: ear, Make, Model, Engine replaced with Period, Teacher, Course

 

***I can't use sharepoint lists as my DB because the school district has that turned off.