diff --git a/containers/backupchecks/src/backend/app/integrations/autotask/client.py b/containers/backupchecks/src/backend/app/integrations/autotask/client.py
index 3a02e6b..ef29b0d 100644
--- a/containers/backupchecks/src/backend/app/integrations/autotask/client.py
+++ b/containers/backupchecks/src/backend/app/integrations/autotask/client.py
@@ -597,37 +597,51 @@ class AutotaskClient:
         if not isinstance(ticket, dict) or not ticket:
             raise AutotaskError("Autotask did not return a ticket object.")
 
-        def _pick(d: Dict[str, Any], keys: List[str]) -> Any:
+        def _pick(d: Dict[str, Any], keys: List[str]) -> tuple[bool, Any]:
+            """Pick first available field from possible field names.
+
+            Returns tuple: (found, value)
+            - found=True if field exists (even if value is None)
+            - found=False if field doesn't exist in dict
+
+            This allows us to distinguish between "field missing" vs "field is null",
+            which is critical for Autotask PUT payloads that require exact values.
+            """
             for k in keys:
-                if k in d and d.get(k) not in (None, ""):
-                    return d.get(k)
-            return None
+                if k in d:
+                    return (True, d[k])
+            return (False, None)
 
-        # Required stabilising fields for safe resolution updates (validated via Postman tests)
-        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"])
+        # Required stabilising fields for safe resolution updates (validated via Postman tests).
+        # Field names are camelCase as per API contract (docs/autotask_rest_api.md section 2.1).
+        # We must copy the EXACT values from GET response to PUT payload, even if null.
+        found_id, ticket_id = _pick(ticket, ["id"])
+        found_issue_type, resolved_issue_type = _pick(ticket, ["issueType", "issueTypeID", "issueTypeId"])
+        found_sub_issue_type, resolved_sub_issue_type = _pick(ticket, ["subIssueType", "subIssueTypeID", "subIssueTypeId"])
+        found_source, resolved_source = _pick(ticket, ["source", "sourceID", "sourceId"])
+        found_status, resolved_status = _pick(ticket, ["status", "statusID", "statusId"])
 
+        # Validate that required fields exist in the response
         missing: List[str] = []
-        if _pick(ticket, ["id"]) in (None, ""):
+        if not found_id or ticket_id in (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 not found_status or resolved_status in (None, ""):
             missing.append("status")
+        if not found_issue_type:
+            missing.append("issueType")
+        if not found_sub_issue_type:
+            missing.append("subIssueType")
+        if not found_source:
+            missing.append("source")
 
         if missing:
             raise AutotaskError(
                 "Cannot safely update ticket resolution because required fields are missing: " + ", ".join(missing)
             )
 
+        # Build payload with exact values from GET response (including null if that's what we got)
         payload: Dict[str, Any] = {
-            "id": int(ticket.get("id")),
+            "id": int(ticket_id),
             "issueType": resolved_issue_type,
             "subIssueType": resolved_sub_issue_type,
             "source": resolved_source,
@@ -648,7 +662,7 @@ class AutotaskClient:
         ]
         for f in optional_fields:
             if f in ticket:
-                payload[f] = ticket.get(f)
+                payload[f] = ticket[f]
 
         return self.update_ticket(payload)
 
diff --git a/docs/changelog-claude.md b/docs/changelog-claude.md
index d41ad62..7c8844f 100644
--- a/docs/changelog-claude.md
+++ b/docs/changelog-claude.md
@@ -4,6 +4,11 @@ This file documents all changes made to this project via Claude Code.
 
 ## [2026-02-05]
 
+### Fixed
+- Autotask ticket resolution update now correctly preserves exact field values from GET response in PUT payload.
+  The `issueType`, `subIssueType`, and `source` fields are copied with their exact values (including null)
+  from the GET response, as required by Autotask API. Previously these fields were being skipped or modified.
+
 ### 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: