Connecting two systems is not just a technical decision. It is a decision about responsibility.
When the same information appears in several places, a business needs to know where that information originates, where it may be changed and which version to trust when records disagree.
Start with the information, not the platform.
Group the information by its purpose. Identity is not the same thing as a business membership. A payment is not the same thing as a reporting metric. A source transaction is not the same thing as a calculated summary.
Giving every category a clear owner makes the system easier to reason about. It also makes the integration requirements more precise.
Distinguish a source from a projection.
A reporting view may combine information from several operational systems. That makes it useful, but it does not automatically make it the authority for the original records.
Keep the relationship understandable: where a record came from, how it was transformed and which source is responsible for correcting it.
Every piece of information should have a clear home, even when it appears in many places.
Decide what happens when records disagree.
What if one platform has an updated status while another is waiting for its next synchronization? What if a record is duplicated? What if an update fails halfway through?
These are design questions. A documented rule is more useful than hoping that the newest timestamp always represents the right answer.
Make the decisions visible.
A simple ownership map can identify the original source, the systems that consume the data, the permitted changes and the recovery path.
It gives developers, operators and business owners a shared reference. Before designing the connection, decide what the connection is responsible for.