Document HTTP 409 response when deleting fields in use by Segments

Signed-off-by: promptless-for-oss <[email protected]>

Author: promptless-for-oss

docs/rest_api/fields.rst

@@ -564,10 +564,16 @@ Delete a field.
 
 ``DELETE /fields/contact/ID/delete`` or ``DELETE /fields/company/ID/delete``
 
+.. note::
+
+   You can't delete a field that's in use by a Segment. This returns an HTTP 409 (Conflict) response. Remove the field from any Segment filters before deleting it.
+
 **Response**
 
 ``Expected Response Code: 200``
 
+``Response Code if field is in use: 409``
+
 **Properties**
 
 Same as `Get Field <#get-field>`_.