diff --git a/containers/backupchecks/src/backend/app/integrations/autotask/client.py b/containers/backupchecks/src/backend/app/integrations/autotask/client.py
index 3a02e6b..e95058a 100644
--- a/containers/backupchecks/src/backend/app/integrations/autotask/client.py
+++ b/containers/backupchecks/src/backend/app/integrations/autotask/client.py
@@ -598,27 +598,32 @@ class AutotaskClient:
             raise AutotaskError("Autotask did not return a ticket object.")
 
         def _pick(d: Dict[str, Any], keys: List[str]) -> Any:
+            """Pick the first available value from a list of possible field names.
+
+            Returns the value (including 0) if found, or None if not present.
+            Note: 0 is a valid Autotask picklist value meaning 'not set'.
+            """
             for k in keys:
-                if k in d and d.get(k) not in (None, ""):
+                if k in d:
                     return d.get(k)
             return None
 
+        def _has_field(d: Dict[str, Any], keys: List[str]) -> bool:
+            """Check if any of the field names exist in the dict."""
+            return any(k in d for k in keys)
+
         # Required stabilising fields for safe resolution updates (validated via Postman tests)
+        # Note: These fields may have value 0 (not set) which is valid and must be preserved.
         resolved_issue_type = _pick(ticket, ["issueType", "issueTypeID", "issueTypeId"])
         resolved_sub_issue_type = _pick(ticket, ["subIssueType", "subIssueTypeID", "subIssueTypeId"])
         resolved_source = _pick(ticket, ["source", "sourceID", "sourceId"])
         resolved_status = _pick(ticket, ["status", "statusID", "statusId"])
 
+        # Only id and status are truly required - others may be 0/null in Autotask
         missing: List[str] = []
-        if _pick(ticket, ["id"]) in (None, ""):
+        if _pick(ticket, ["id"]) is None:
             missing.append("id")
-        if resolved_issue_type in (None, ""):
-            missing.append("issueType")
-        if resolved_sub_issue_type in (None, ""):
-            missing.append("subIssueType")
-        if resolved_source in (None, ""):
-            missing.append("source")
-        if resolved_status in (None, ""):
+        if resolved_status is None:
             missing.append("status")
 
         if missing:
@@ -628,27 +633,28 @@ class AutotaskClient:
 
         payload: Dict[str, Any] = {
             "id": int(ticket.get("id")),
-            "issueType": resolved_issue_type,
-            "subIssueType": resolved_sub_issue_type,
-            "source": resolved_source,
             # Keep status unchanged
             "status": resolved_status,
             "resolution": str(resolution_text or ""),
         }
 
-        # Copy other stabilising fields when available (helps avoid tenant-specific validation errors)
-        optional_fields = [
-            "companyID",
-            "queueID",
-            "title",
-            "priority",
-            "dueDateTime",
-            "ticketCategory",
-            "organizationalLevelAssociationID",
+        # Copy stabilising fields when present in the response (even if value is 0/null)
+        # This preserves the current ticket classification without unintended changes.
+        stabilising_fields = [
+            ("issueType", ["issueType", "issueTypeID", "issueTypeId"]),
+            ("subIssueType", ["subIssueType", "subIssueTypeID", "subIssueTypeId"]),
+            ("source", ["source", "sourceID", "sourceId"]),
+            ("companyID", ["companyID"]),
+            ("queueID", ["queueID"]),
+            ("title", ["title"]),
+            ("priority", ["priority"]),
+            ("dueDateTime", ["dueDateTime"]),
+            ("ticketCategory", ["ticketCategory"]),
+            ("organizationalLevelAssociationID", ["organizationalLevelAssociationID"]),
         ]
-        for f in optional_fields:
-            if f in ticket:
-                payload[f] = ticket.get(f)
+        for field_name, keys in stabilising_fields:
+            if _has_field(ticket, keys):
+                payload[field_name] = _pick(ticket, keys)
 
         return self.update_ticket(payload)
 
diff --git a/docs/changelog-claude.md b/docs/changelog-claude.md
index d41ad62..e8358f7 100644
--- a/docs/changelog-claude.md
+++ b/docs/changelog-claude.md
@@ -4,6 +4,12 @@ This file documents all changes made to this project via Claude Code.
 
 ## [2026-02-05]
 
+### Fixed
+- Autotask ticket resolution update now correctly handles tickets where `issueType`,
+  `subIssueType`, or `source` fields are not set (value 0 or null). Previously this
+  caused "required fields are missing" errors. Now only `id` and `status` are required;
+  other stabilising fields are copied when present.
+
 ### Added
 - Restored Autotask PSA integration from branch `v20260203-13-autotask-resolution-item-wrapper`:
   - `integrations/autotask/client.py` - Autotask REST API client with full support for: