Hi,
I’ve migrated open AP / AR many times.
If the real need is to migrate open AP, then maybe simply consider the open supplier payment on account just like any other invoice. Same is true for the AR, Migrate as an open invoice. If we consider the IFS flow for advance payments / advance customer invoices, these open on account values (in IFS) would normally be connected with a source item. That connection is really hard to replicate via migration.
My clients (even the largest with hundreds of open payment on account) had chosen to migrate as open items (like an invoice) and then after go live manually use these with the corresponding records. If I recall correctly one of my clients had thousands of these open payments on account.
Perfect world, your client should have many months to clean this up before the final migration. Cleaner data, less of these open items exist.
You can include a good deal of information on each of the item records. NCF reference is commonly used, it’s very visible in IFS screens and the attribute is large enough for good documentation.
Best regards,
Thomas