Industries CPQ: Order submission fails with message "Submit Failed on the remote action vlocity_cmt.CPQAppHandler.checkout"

PFB the details of Possible RCA of the issue:-

Cause 1: Required cart attributes aren't configured on the order line items

1. Open the affected order and click Configure button to launch the Hybrid CPQ/LWC Cart.
2.  For each order product, open the line item and review every required attribute on the Attributes tab. Required attributes are flagged in the Cart UI with a red indicator.
3.  Populate every required attribute with a valid value, then click Save.
4.  Re-run the Integration Procedure that calls vlocity_cmt.CPQAppHandler.checkout.

Cause 2: Order Status or Fulfilment Status isn't in a submittable state

1. Open the order record and inspect Order Status [vlocity_cmt__OrderStatus__c] and Fulfilment Status [vlocity_cmt__FulfilmentStatus__c].
2.  If either field is set to Rejected, Activated, or any value other than Ready To Submit / Draft, update both fields to Ready To Submit using a DataRaptor or anonymous Apex. Required values for re-submission: vlocity_cmt__OrderStatus__c = Ready To Submit, vlocity_cmt__FulfilmentStatus__c = Draft.
3.  Re-run the Integration Procedure and confirm decomposition and the Orchestration Plan are generated.

Cause 3: Order Management license or XOM Administration is not configured

1.  From Setup, in the Quick Find box, enter Installed Packages and verify the Communications, Media, and Energy & Utilities managed package and the Order Management license are present and active.
2.  From the App Launcher, open Vlocity CMT Administration (or Industries CME Administration) and click XOM Administration.
3.  In sandboxes refreshed from Production, run Setup > Company Information > Match Production Licenses to pull the OM license into the sandbox.
4. Retry the submission.

Cause 4: LoggingEnabled is true and submission hits Apex CPU time limit Exception

1. Navigate to Setup > Custom Settings > General Setting > Manage.
2. Locate LoggingEnabled and set its Value to false. Click Save.
3.  If submission still times out for large orders, navigate to the same Custom Settings named XOM SetUp page and set OrderSubmitMode to Queuing so decomposition and orchestration plan composition run asynchronously.
4.  Retry the submission and monitor Setup > Apex Jobs for jobs named XOMOrderEventProcessor.

Cause 5: Integration Procedure remote action references the wrong namespace

1. Open the Integration Procedure in OmniStudio Integration Procedures.
2. On the Remote Action step, set Remote Class to vlocity_cmt.CpqAppHandler (with the vlocity_cmt namespace prefix) and Remote Method to checkout.
3. Save and activate the Integration Procedure, then retry.