What is patient ID -1 in the online scheduler appointment requests?
This indicates that the patient who scheduled the appointment is a new patient, and does not exist in your practice management software.
You will the need to create this new patient in the Practice Management Software (PMS) as a patient of record.
After that, click Settings > Online Scheduler Settings > Online Patients to complete the "linking" of the new patient. See article on Online Patients for details.