If your Flow includes a DML element such as Create, Update or Delete records, or a Submit for Approval core action, then there is a possibility that it might fail. For example, a create or update may fail if it does not pass the validation rule. And when the flow fails, Salesforce displays a standard message in red text that reads “An unhandled fault has occurred in this flow”. But with an error message like this, users will have no clue of what happened and if they did anything wrong.

A better option is to use something called ‘Fault’ path in Flow. Fault Path is also called Fault Connector or Fault Line. With Fault path, you can display a more meaningful message and guide users on what to do. To create a fault path, create a screen element with useful message and connect it to the DML element. 

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Custom Permissions in Salesforce are used to give access to users for certain apps or processes that you have configured and which cannot be controlled by profile or permission set directly.

A profile and a permission set control the users’ access to many entities such as objects, fields, tabs, and Visualforce pages. However, they cannot control a custom process that you have which is unique to your business. For e.g. only specific users should be able to edit an Opportunity once it is Closed Won or save records bypassing validation rules. To manage these granularities, you can leverage Custom Permissions in Salesforce. They let you define checkpoints that can be assigned to users via permission sets or profiles, in the same way how other permissions are assigned to users.

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