This KB explains the Apstra pristine validation when onboarding Junos and Junos-EVO devices.

Having a management-instance in the pristine for Junos and Junos-EVO devices is mandatory since Apstra 4.2. If you don't have it, pristine validation in the device onboarding should fail. You can configure a management-instance as shown in the 'Juniper Junos Offbox Agent Minimum Configuration' example, and retry onboarding again. 

In addition, some configurations could raise pristine validation errors. Make sure the following configuration is not on the devices (and any other configuration that would raise validation errors):

 - VLANs other than VLAN 1

 - VRFs other than "management"

 - Interface IP addresses other than "management"

 - Loopback interfaces

 - VLAN interfaces

 - VXLAN interfaces

 - AS-Path access-lists

 - IP prefix-lists

 - Route maps or policies

 - BGP configuration

 Please see the Apstra documentation 'Create Offbox Agent' section for details. 

 https://www.juniper.net/documentation/us/en/software/apstra6.1/apstra-user-guide/topics/task/agent-offbox-create.html#device_agents_creating_off-box_agent__subsection_gkl_xzg_zcc