Send (or resend) a one-time code via SMS to the customer's phone number to begin phone verification.

This endpoint is only meaningful for customers whose payment provider requires contact verification (e.g. EU customers); the customer's contactVerification.phone status reflects progress. For customers whose provider has no such requirement, this returns 409.

Call POST /customers/{customerId}/verify-phone/confirm with the received code to complete verification. Re-POST this endpoint to resend the code.

In sandbox, no SMS is sent and the code is always 000000.