If clients are reporting that they can't to leave a review for your business, it is likely because the Review Request email is not automatically triggering to the client after their appointment.
In order for a Review Request to send automatically, appointments need to be checked out within the number of days that your Review Request email is set to send based on your Review Request Settings. If an appointment is checked out outside of the window that it is scheduled to send, the Review Request will not trigger.
For example, if your Review Request settings are set to send three days after check out, you will want to ensure that you check out the appointment within three days of the appointment date. Appointments checked out four days after the appointment date will not initiate a Review Request.
If you are checking out appointments within the allotted window and your client is not receiving their review request, you will want to ensure that the Review Request alert is enabled under Settings > Outgoing Messages > Client Messages.