Hi @courtneyts, Source is included in the “Default Fields” section of Lead Configuration, and is limited to a single source for all Leads created by the integration. We implemented this based on customer feedback and requests to set a consistent Source value for the leads we create.
We do allow mapping of CallRail Source and/or utm_source fields to a custom field on the Lead in Salesforce, which I’ve seen many customers do. That field value would be dynamically set for each lead based on the source we determine for that lead (in part based on the number called).
If it is critical to your workflow to specifically set the Source field dynamically, I believe this could be done by mapping CallRail Source to a custom field on the Lead, and then setting the Lead Source to the same value as the custom field through a Field Update Workflow in Salesforce.
This Salesforce help article might be useful: https://help.salesforce.com/articleView?id=workflow_managing_field_updates.htm&type=5