Expression to get list from multi related tables

I have a Bank Accounts table as under:

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What I am trying to achieve is to get a list of Account Codes (as “Suggested Values” under Auto Compute for the Account Code field) relevant to the Co Code (as defined in the Co Code field above) though multi related tables as under:
(1) The Co Code field in the above table has a Ref to the Companies table as under:

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(2) Each Company set up in the above table can have multiple Set of Books (SOB) and the relationship is through the Assign SOB to Companies table as below

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(3) Each SOB is related to a Chart of Accounts (COA) as under in the Set of Books Table through the COA Id field

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(4) Each Chart of Accounts is related to a COA Lines Table as under: One COA Header record can have multiple COA Lines

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(5) Finally the COA Lines table is as under which has Account Code as a field

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So what is the simplest way of achieving this through dereference / reverse dereference expressions as writing multiple nested SELECTs will be complex

Tried various things but keep getting an error saying reference not found

Any help please will be appreciated. Its beyond my current level of proficiency :blush:

Set Valid_If in [Co Code] to:
[Related Bank Accounts][Co Code]