Implementing accounts payable in an ERP system goes wrong in a predictable order, and the pattern is consistent enough to plan around. What derails go-live is almost never the accounting configuration, which is well understood and usually done carefully. It is the supplier master coming across dirty, approvers not being ready, and open items being migrated without their history. This page is what to settle before go-live, what genuinely can wait until afterwards, and the argument for a parallel month that project plans usually cut and teams usually wish they had kept.
Settle before go-live: supplier master and approvers
Clean the supplier master before migration rather than after, because duplicates and dead suppliers multiply once there is history. And have approvers trained and tested on their actual devices, since an approval process nobody can use on day one produces a paper workaround that becomes permanent.
What can wait
Automation rules, sophisticated tolerances, and reporting beyond the essentials. Go live with the process you have and tighten afterwards; a go-live that also changes how people work has two failure modes instead of one.
Insist on a parallel month
One month run in both systems, with the payables balance reconciled between them at the end. It is the only test that proves the migration was complete, and it is the first thing cut when a plan slips. On the worked example on this site, 400 invoices at three touches of six minutes with a 12% exception rate is 134.4 hours a month: $4,300.80 at a $32 loaded rate, $10.75 an invoice and $51,609.60 a year.
Questions people ask about erp system accounts payable
How long does payables implementation take?
Longer than the accounting configuration suggests, because the supplier data and the people are the work. Plan around those two rather than around the module.
Should we migrate open invoices or start clean?
Migrate open items with enough history that a supplier query can be answered. Starting completely clean means answering queries from the old system for a year, which is a hidden cost.
What is the commonest go-live problem?
Approvers unable to approve. It looks like a training issue and is usually an access or device issue, and it should have been found in testing.