how to use ‘belong to’ filter in acumatica report design

You state that BelongsTo is not a standard filter type in Acumatica but it is used in some reports.  For example in Payrol report PR641060.rpx it is used.  However, I cannot find any help on how it works.

I recently had this same question while working on the report designer with the ‘belongs to’ condition.

This is a very specific condition from the framework that is used to identify the Branches associated to a given Organization/Company’s BaccountID value.

All references to this condition in the standard Acumatica reports show the pattern Branch belongs to OrgBAccountID. Here is an example from one of the 1099 reports

What is occurring underneath during this SQL representation is that the parameter displays the one - or many - BranchID associated to said Business Account.

Notice that the SQL representation of the query converted the second parameter to this result:

AND [CompanyBranchBAccount1099_BAccountR].[BAccountID] = 7128 AND [AP1099History].[BranchID] IN ( 125, 29, 66))

Be aware that belongs to and IN are not the same. IN condition does not replace the value.
If we change the example above to use IN instead, this is the SQL representation (which will not print correct results)

AND [CompanyBranchBAccount1099_BAccountR].[BAccountID] = 7128 AND [AP1099History].[BranchID] IN ( 7128))