Platform conversions are not cash. They are the last event the vendor can see. For most mid-sized service businesses the valuable event is a conversation, a close, and an invoice. Those live in other products.
Where the chain actually breaks
UTM dies at the form. The call never writes back. Stripe cannot find the CRM person. Each break is small. Together they make the channel report a story about the top of a broken chain.
The join work that has to happen first
Capture source on purpose at the form, the calendar, and the first conversation. Write the call onto the opportunity. Attach the billing customer to the same person. Then report attributed cash and unattributed cash as two numbers.
If half of closed revenue has no source, the job is capture, not a new campaign and not a multi-touch model.
Unknown is a job
A complete-looking pie that hides unknown source is literature. Coverage is the first metric. Experiments wait until the chain can lose.