Filter second drop down list

Hi All, please could you give some background?

I am working in layout FactoryAllocations.

I have a drop down with records from my ATA Table

my second drop down is from the FactoryPrice, but I only want to see part with the same ATA as selected in the first drop down.

I have my relationship, Factory Price and ATA tbl with relationship between ATAChapter

I have created a second bable instance for FactoryPrice and linked to ATA - ATAChapter

In my second drop down, I Use value from the  FactoryPrice_ATA Tbl and only include values starting from ATA.

Still I get all record and not filtered.

Is my understanding of this incorrect?