Problem

I would like to map data between Magento and Salesforce, however I am not seeing a custom field I created in Salesforce

Solution

Check the field security settings in Salesforce. A field should be visible for the API user used for synchronization. See example below:
1. Navigate to "Setup" > "App Setup" > "Customize" > "Order" > "Fields"
2. Click on "Bill To Contact" link (NOT the "Edit" next to it, but the actual name)
3. Click on "Set Field Level Security"
4. Make sure the field is "visible" to API user and make sure the field is NOT "read only"
Re-generate WSDL file in Salesforce and upload it to Magento server:
1. Navigate to "Setup" > "App Setup" > "Develop" > "API"
2. Click on "Generate Enterprise WSDL"
3. Click on "Generate" button
4. Right-click on the page and choose "Save As ..." and save the file to your local drive
5. Upload to your Magento environment and clear "Salesforce Cache" in Magento
  1. In Magento, navigate to "System" > "Cache Management"
  2. Check "Salesforce" row, choose "Refresh" Action and click "Submit"