diff --git a/app/models/case_log.rb b/app/models/case_log.rb
index 723dbeceb..0ef775c11 100644
--- a/app/models/case_log.rb
+++ b/app/models/case_log.rb
@@ -38,6 +38,12 @@ class CaseLogValidator < ActiveModel::Validator
       record.errors.add :other_reason_for_leaving_last_settled_home, "The other reason must not be provided if the reason for leaving settled home was not other"
     end
   end
+  
+  def validate_reason_for_leaving_last_settled_home(record)
+    if record.reason_for_leaving_last_settled_home == "Do not know" && record.benefit_cap_spare_room_subsidy != "Do not know"
+      record.errors.add :benefit_cap_spare_room_subsidy, "must be do not know if tenant’s main reason for leaving is do not know"
+    end
+  end
 
   def validate_net_income(record)
     return unless record.tenant_economic_status && record.weekly_net_income
diff --git a/config/forms/2021_2022.json b/config/forms/2021_2022.json
index 47378e9f0..1d2d72b57 100644
--- a/config/forms/2021_2022.json
+++ b/config/forms/2021_2022.json
@@ -612,7 +612,7 @@
               "header": "Leaving their last settled home",
               "description": "",
               "questions": {
-                "last_settled_home": {
+                "reason_for_leaving_last_settled_home": {
                   "header": "What is the tenant’s main reason for leaving?",
                   "hint_text": "",
                   "type": "radio",
diff --git a/docs/api/DLUHC-CORE-Data.v1.json b/docs/api/DLUHC-CORE-Data.v1.json
index 015e98a07..374c30bfb 100644
--- a/docs/api/DLUHC-CORE-Data.v1.json
+++ b/docs/api/DLUHC-CORE-Data.v1.json
@@ -193,7 +193,7 @@
         "summary": "Create New Case Log",
         "operationId": "post-caselog",
         "responses": {
-          "200": {
+          "201": {
             "description": "Case Log Created",
             "content": {
               "application/json": {
@@ -781,11 +781,55 @@
           },
           "reason_for_leaving_last_settled_home": {
             "type": "string",
-            "minLength": 1
+            "minLength": 1,
+            "enum": [
+              "Permanently decanted from another property owned by this landlord",
+              "Left home country as a refugee",
+              "Loss of tied accommodation",
+              "Domestic abuse",
+              "(Non violent) relationship breakdown with partner",
+              "Asked to leave by family or friends",
+              "Racial harassment",
+              "Other problems with neighbours",
+              "Property unsuitable because of overcrowding",
+              "End of assured shorthold tenancy - no fault",
+              "End of assured shorthold tenancy - tenant's fault",
+              "End of fixed term tenancy - no fault",
+              "End of fixed term tenancy - tenant's fault",
+              "Repossession",
+              "Under occupation - offered incentive to downsize",
+              "Under occupation - no incentive",
+              "Property unsuitable because of ill health / disability",
+              "Property unsuitable because of poor condition",
+              "Couldn't afford fees attached to renewing the tenancy",
+              "Couldn't afford increase in rent",
+              "Couldn't afford rent or mortgage - welfare reforms",
+              "Couldn't afford rent or mortgage - employment",
+              "Couldn't afford rent or mortgage - other",
+              "To move nearer to family / friends / school",
+              "To move nearer to work",
+              "To move to accomodation with support",
+              "To move to independent accomodation",
+              "Hate crime",
+              "Death of household member in last settled accomodation",
+              "Discharged from prison",
+              "Discharged from long stay hospital or similar institution",
+              "Other",
+              "Do not know",
+              "Prefer not to say"
+            ]
           },
           "benefit_cap_spare_room_subsidy": {
             "type": "string",
-            "minLength": 1
+            "minLength": 1,
+            "enum": [
+              "Yes - benefit cap",
+              "Yes - removal of the spare room subsidy",
+              "Yes - both the benefit cap and the removal of the spare room subsidy",
+              "No",
+              "Do not know",
+              "Prefer not to say"
+            ]
           },
           "armed_forces_active": {
             "type": "string",
@@ -1158,4 +1202,4 @@
     },
     "securitySchemes": {}
   }
-}
+}
\ No newline at end of file
diff --git a/spec/models/case_log_spec.rb b/spec/models/case_log_spec.rb
index bb217fa75..f9e33afd7 100644
--- a/spec/models/case_log_spec.rb
+++ b/spec/models/case_log_spec.rb
@@ -81,7 +81,14 @@ RSpec.describe Form, type: :model do
         }.to raise_error(ActiveRecord::RecordInvalid)
       end
     end
-
+    context "reason for leaving last settled home validation" do
+      it "Reason for leaving must be don't know if reason for leaving settled home (Q9a) is don't know." do
+        expect {
+          CaseLog.create!(reason_for_leaving_last_settled_home: "Do not know",
+                          benefit_cap_spare_room_subsidy: "Yes - benefit cap")
+        }.to raise_error(ActiveRecord::RecordInvalid)
+      end
+    end
     context "other reason for leaving last settled home validation" do
       it "must be provided if main reason for leaving last settled home was given as other" do
         expect {