Cascading Drop Down SP Form - Retrieving Items from a Foreign Table

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I'm using a PowerApps trial to see if I can help justify the cost to my department. I created a series of SharePoint lists:

Table 1: tbl_Meeting   

Fields: Titles Meeting Title

Table 2: tbl_MeetingDateTime

Fields: Meeting Title(lookup),  MeetingDateTime

Table3:tbl_Agenda Items

Fields: MeetingTitle(lookup), MeetingDateTime(lookup), Title...)    Note: MeetingTitle & MeetingDateTime are site columns

I'm trying to create a PowerApps form for Table 3 that has cascading drop down where you select the Meeting Title and then it filters the MeetingDateTime field to only show the times where there is a record matching the same meeting title in Table2. Is this possible?

I have connected the Table 2 & Table 3 to the app but when I try and get the DateTime items from tbl.MeetingDateTime, PowerApps seems to not like this.

Any advice appreciated.

Thanks,