1. Write down exactly what should move
List the records involved, such as customers, orders or invoices, and for each one the fields that need to reach the other system. Note which direction each field travels and how quickly it needs to arrive. Anything not on the list stays where it is.
This list becomes the specification for the whole connection, and it is the first thing to check when something looks wrong later.
2. Decide how records are matched
Before data moves, each system must be able to tell whether a record already exists on the other side. Decide what identifies the same customer or order in both systems:
- A shared ID stored in both systems is the most reliable
- An email address or account number works if it is unique and rarely changes
- Names alone are not safe: people share names and spell them differently
Weak matching is the most common cause of duplicate records after a connection goes live.
3. Choose a source of truth for every field
When the same field exists in both systems, decide which one wins if they disagree. Billing details might belong to the accounting system, while contact details belong to the CRM. Write the rule down for every shared field.
Also decide what happens when a field changed in both places since the last sync. The safe answer is to hold it for a person rather than let one change silently overwrite the other.
4. Test on copies, not on live data
Use test accounts or sandbox environments if the systems offer them, or a copy of a small set of real records. Test the cases that break connections:
- A brand new record and an update to an existing one
- A record with a missing or oddly formatted field
- The same record edited in both systems
- The same request sent twice, which must not create two records
5. Plan the backfill of existing records separately
Connecting two systems that already hold data means deciding what happens to the records created before the connection. Matching thousands of historical records is different from syncing new ones and deserves its own dry run, with a count of how many will be created, updated and skipped before anything is written.
6. Plan for failure before it happens
Every connection will eventually hit an expired login, a vendor outage or an unexpected value. Decide in advance:
- Who gets alerted, and how quickly
- How failed records are retried without creating duplicates
- Where a log of every sync is kept and who can read it
- How to pause the connection quickly if something goes wrong
7. Use the least access that works
Give the connection its own account or key, with only the permissions it needs, rather than a person’s login. It keeps the connection working when that person leaves and limits what a mistake can touch. Keep those credentials in accounts you control.
8. Go live in stages and watch it
Start with a small group of records or a single location, compare both systems by hand for the first days, and widen the scope once the counts agree. A connection that has run cleanly for a few weeks under watch is one you can stop checking every day.