Need help with Numbers formula

This should be fairly easy, but without seeing your formula it's hard to tell what's wrong.

Given what you showed, the formula in Master::Table 1::C2 should be:

=VLOOKUP($A2,remote::Table 1::A:B,2,FALSE)

VLOOKUP() takes 4 arguments. The first is the value you want to lookup - in this case, cell $A2

The second argument is the range you want to search - this needs to include not only the ID column, but also the values (totals) column, so I have it set to columns A:B from Table1 on the 'remote' sheet ('remote::table1::A:B)

The third argument is which column you want to return the value from - in this case you want column B, or the 2nd column in the range, hence the '2'.

Lastly comes a TRUE/FALSE flag which toggles exact/closest match. In this case you presumably want an exact match, hence FALSE.

The mistake most people make with VLOOKUP is that they only include the search range as the second parameter, not the search-and-results range. That's where XLOOKUP is preferable, where you can specify distinct lookup and results ranges, as well as what to do for missing matches. A comparable XLOOKUP might say:

=XLOOKUP($A2,remote::Table 1::A,remote::Table 1::Order total,"MISSING ID",0,1)