Single Table Multi Column Validation List Not Working

I'm trying, unsuccessfully, to create 2 validation lists based on a table.  I would like this to work on a row by row basis.  The validation list based on the table headers works fine, the secondary validation doesn't work at all.

Goal: To create a dropdown in the material column that will only display the material type on row 2 of the table based on a match.  

Looking @ the example, row two Material (NTX Disposal Log!D2) would display a validation list based on the entry in the Disposal Site Column (NTX Disposal Log!B2) by matching the the entry to a table header in the LF_MAT table and returning the values below the matched value, in this case, City of Denton, which would return a validation list selection of MSW.

I was trying to follow the instructions laid out here:
https://www.excel-university.com/use-the-column-header-to-retrieve-values-from-an-excel-table/

What I don't understand is how to adapt

=INDEX(tbl_choices,,MATCH(region,dd_regions,0))

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to

=INDEX(LF_MAT,,MATCH(material,LF_DROPDOWN,0))

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Table Name: LM_MAT (tbl_choices in the web instructions)
Named Range: LF_DROPDOWN (=LF_MAT[#Headers]) (dd_regions in the web instructions)
Name Rage: MAT_DROPDOWN (=INDEX(LF_MAT,,MATCH(MATERIAL,LF_DROPDOWN,0)) (dd_reps in the web instruction
Disposal Site Validation: =LF_DROPDOWN (works fine)
Material Validation: =MAT_DROPDOWN (doesn't work @ all)

NTX Disposal Log-Combined-Running.xlsx

Any help would be greatly appreciated.