Greatly reduce repeated code

functions/api/data-transfers/create.ts

@@ -1,3 +1,5 @@
+import { jsonError } from "../../common.js";
+
 export async function onRequestPost(context: RequestContext) {
   const { cookie, has_access } = context.data.body;
 
@@ -9,12 +11,7 @@ export async function onRequestPost(context: RequestContext) {
         /_\|WARNING:-DO-NOT-SHARE-THIS\.--Sharing-this-will-allow-someone-to-log-in-as-you-and-to-steal-your-ROBUX-and-items\.\|_[A-F\d]+/,
       ))
   )
-    return new Response('{"error":"Invalid request"}', {
-      headers: {
-        "content-type": "application/json",
-      },
-      status: 400,
-    });
+    return jsonError("Invalid request", 400);
 
   const id =
     (context.request.headers.get("cf-ray")?.split("-")[0] as string) +
@@ -53,13 +50,7 @@ export async function onRequestPost(context: RequestContext) {
     },
   );
 
-  if (!authedUserReq.ok)
-    return new Response('{"error":"Cookie is invalid"}', {
-      headers: {
-        "content-type": "application/json",
-      },
-      status: 400,
-    });
+  if (!authedUserReq.ok) return jsonError("Cookie is invalid", 400);
 
   const authedUser: { id: number; name: string } = await authedUserReq.json();
 
@@ -79,13 +70,7 @@ export async function onRequestPost(context: RequestContext) {
     },
   );
 
-  if (!createCardReq.ok)
-    return new Response('{"error":"Failed to create entry"}', {
-      headers: {
-        "content-type": "application/json",
-      },
-      status: 500,
-    });
+  if (!createCardReq.ok) return jsonError("Failed to create entry", 500);
 
   await context.env.DATA.put(
     `datatransfer_${id}`,