Each supplier has delivered its own component, yet the combined result does not work. A multi-supplier interface needs an agreed input and output boundary, ownership of the joining work and evidence that the pieces function together. Separate supplier task lists do not automatically provide that agreement.
PMI's requirements guidance supplies the wider acceptance context. The interface record below is an original coordination tool, not a contract template or a technical standard.
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Define the boundary in operational terms
Ask what crosses between suppliers: a file, design, physical component, approved information or a completed service action. Describe its meaning, version, format and conditions of use with the relevant specialists.
Identify the receiving owner. A provider can meet its own interpretation while the receiver expects something else. Bring both sides into the definition before their internal work becomes expensive to change.
Use a shared interface record
Capture:
Item supplied and its intended use.
Provider, receiver and internal coordinating owner.
Required structure, version and agreed definitions.
Preconditions, access and timing.
Validation method and representative test case.
Failure, correction and escalation ownership.
Change-notification route and approval authority.
Do not leave the interface assigned to both suppliers collectively. They can share work, but the business still needs a named route for resolving a gap that falls between their scopes.
A hypothetical data handoff
One supplier provides booking data; another builds the reporting view. Both use a field named date, but one means request creation and the other assumes appointment date. The file arrives on time and opens correctly, yet the resulting report answers the wrong business question.
A joint interface check uses a representative case and confirms the field's meaning. The business owner resolves which date the report needs, the suppliers agree the mapping and the project records how future changes reach both sides.
This example is deliberately simple. A successful file transfer alone would not reveal the semantic mismatch.
Test the joining work early
Choose a proportionate early test that can expose mismatched assumptions before full delivery. Record what is simulated and what remains untested. A small sample can reveal a problem without proving every later case will pass.
Include an unsuitable or changed input where relevant. Identify who recognises failure and who tells the other supplier. Otherwise the first live exception may sit between two support desks.
Keep scope and commercial gaps visible
If neither supplier's agreement includes necessary integration work, obtain the appropriate business and commercial decision. Do not direct unapproved additional work or decide contractual responsibility from the interface spreadsheet.
The small-team project plan connects interface checks to dependencies and dates. For the connected task, read How to Write Project Acceptance Criteria People Can Actually Check. If separately completed supplier outputs fail at the join, discuss your project requirements.
