In order to ensure that case records are shared out to your shared queue and then eventually on to ServiceNow, you will need to create a dynamic share on the Salesforce side.
Prerequisites
Install the Perspectium Package for Salesforce
Configure your Salesforce remote site settings
Configure Perspectium Replicator as a Salesforce connected app
Configure Perspectium properties for Salesforce
Create a Salesforce shared queue
Procedure
To create a dynamic share in Salesforce, follow these steps:
Log into your Salesforce organization and click the 
icon in the upper left-hand corner of the screen. Then, click the Perspectium Replicator app.
In the navigation bar near the top of the screen, click Dynamic Shares. In the upper left-hand corner of the resulting page, click New Dynamic Share.
From the Table dropdown, choose Case. Then, check the Active box to start sharing out case records dynamically.
Check the Create box to dynamically share Salesforce case record data that is newly created. Check the Update box to dynamically share Salesforce case record data that is updated. Finally, check the Delete button to ensure that deleted Salesforce case records no longer appear in your ServiceNow instance. Optionally, you can check Include Attachments if you want to dynamically share out attachments that are added to your Salesforce case records. You also have the option to create Filters here for your Salesforce dynamic share if you wish.
Choose AES-128 or AES-256 as an encryption cipher, or choose Base64 to have base 64 encoding only for your dynamically shared data.
For the Target Queue, choose psp.in.siam.provider.salesforce.
Scroll down to the bottom of the Dynamic Share form and click Save. All other required fields will then be created automatically. To complete the configuration of your Salesforce dynamic share, click Save Trigger.
