Table Relationships - Connected CSV Table

So the main issue here is that your 'Orders' table is not using Order # as the primary key. The Order # is a field that matches in both tables but as it shows in your relationship screenshot the primary key in the Orders table is the Quickbase built in Record ID#. Why this matters then is that Quickbase is trying to match the that value from the Orders table to a matching value in the Child table - in this case the foreign key or 'Related Order'. To demonstrate: 

Order #2023029.0D0 - lets say in QB has a Record ID# of 100 as an example. With your relationship - Quickbase is trying to match the Record ID# value of 100 to the Related Order value in your Actuals table and a matching value of 100. 

How you solve that then is a matter of how you want to handle your keys. Option 1 is to change the primary key of your orders table to be the Order #. Doing so can dramatically change your app - and requires that you always keep that # unique and that you have a way to populate it when you're creating new orders. If you do this though - then the Key field of Orders will no longer be Record ID# and instead be the actual Order # and you can then use the matching Order # in the child table to be the foreign key that links them together. 

Your other option - is to leave the key field structure as is, and instead either manually update the value of 'Related Order' or automate the process to update it when you sync the data. What this looks equates to downloading into Excel the Orders data including the Order # and Record ID# as the 2 columns. You can then download the child Actuals data Order # column - and do a vlookup from your orders data to get the associated record ID# of that Order to then populate the value of Related Order. I'll try and demonstrate below with an example: 

Export of Orders Data:

Order #        Record ID #

ABC             1

DEF             2

GHI              3

JKL              4

Import of Actuals Data: 

Order #             Related Order

ABC                          1

ABC                          1

ABC                          1 

DEF                           2

DEF                           2

DEF                           2

GHI                            3

You can manually do this and do the vlookup yourself to find the Record ID# value of the order to import into Related Order - or you can use any combination of formula queries, pipelines, table to table imports to automate that process for you.