Restrict changes to the Close state when the Change Task is open

Server-Side Components/Business Rules/Prevent closure if change tasks are open/Before_BR.js

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+function executeRule(current, previous /*null when async*/){
+  if(current.close_code){
+    var taskGR = new GlideRecord('change_task');
+    taskGR.addQuery('change_request', current.sys_id);
+    taskGR.addQuery('state', '!=', '3') // Adjust as needed
+    taskGR.query();
+
+  if (taskGR.hasNext()){
+    gs.addErrorMessage('You cannot close this change request until all change tasks are closed.');
+    current.setAbortAction(true); // Prevent saving the form
+   }
+ }
+
+})(current, previous);

Server-Side Components/Business Rules/Prevent closure if change tasks are open/README.md

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+Prevent Closure if the change tasks are open
+
+1. Create a Before Business Rule.
+2. Applicable to Change Request Table.
+3. Use Before - Update.
+4. Add conditions if required.
+5. Apply the script.