diff --git a/backend/src/services/External/HitphoneServices/ClientExists.ts b/backend/src/services/External/HitphoneServices/ClientExists.ts
new file mode 100644
index 0000000..d17841b
--- /dev/null
+++ b/backend/src/services/External/HitphoneServices/ClientExists.ts
@@ -0,0 +1,32 @@
+import { cache } from "./utils/cache";
+import authConfig from "../../../config/auth";
+import { responseOk } from "./utils/fetch";
+
+export const fetchWithKey: typeof fetch = async (endpoint, options) => {
+  const response = await fetch(authConfig.hitphone.CLIENT_SERVICE_URL + endpoint, {
+    ...options,
+    headers: {
+      ...options?.headers,
+      "X-Api-Key": authConfig.hitphone.CLIENT_SERVICE_API_KEY,
+    },
+  });
+
+  return response;
+};
+
+const CLIENT_EXISTS_CACHE_TTL = 10 * 1000 * 60;
+const clientExistsCache = cache<boolean>(CLIENT_EXISTS_CACHE_TTL);
+
+export const clientExists = async (id: string): Promise<boolean> => {
+  const fetcher = async (id: string) => {
+    const response = await fetchWithKey(`/clients/${id}`, { method: "HEAD" });
+
+    await responseOk(response);
+
+    return true;
+  };
+
+  const exists = await clientExistsCache.get(id, () => fetcher(id));
+
+  return exists;
+};
\ No newline at end of file
diff --git a/backend/src/services/External/HitphoneServices/utils/cache.ts b/backend/src/services/External/HitphoneServices/utils/cache.ts
new file mode 100644
index 0000000..559b9f0
--- /dev/null
+++ b/backend/src/services/External/HitphoneServices/utils/cache.ts
@@ -0,0 +1,35 @@
+export const cache = <T>(ttl: number) => {
+  type Cache = { promise: Promise<T>, timestamp: number };
+  const store = new Map<string, Cache>();
+
+  const get = async (key: string, fetcher: () => Promise<T>) => {
+    if (store.has(key)) {
+      const cached = store.get(key)!;
+
+      if (Date.now() - cached.timestamp < ttl) {
+        return cached.promise;
+      } else {
+        store.delete(key);
+      }
+    }
+
+    try {
+      const promise = fetcher();
+
+      store.set(key, {
+        promise,
+        timestamp: Date.now()
+      });
+
+      return promise;
+    } catch (error) {
+      store.delete(key);
+
+      throw error;
+    }
+  }
+
+  return {
+    get
+  };
+};
\ No newline at end of file
diff --git a/backend/src/services/External/HitphoneServices/utils/fetch.ts b/backend/src/services/External/HitphoneServices/utils/fetch.ts
new file mode 100644
index 0000000..3495fc1
--- /dev/null
+++ b/backend/src/services/External/HitphoneServices/utils/fetch.ts
@@ -0,0 +1,17 @@
+export class FetchClientsApiError extends Error {
+  public statusCode: number;
+
+  constructor(message: string, statusCode: number) {
+    super(message);
+
+    this.statusCode = statusCode;
+    this.name = "FetchClientsApiError";
+  }
+}
+
+export const responseOk = async (response: Response) => {
+  if (!response.ok) {
+    const message = await response.text();
+    throw new FetchClientsApiError(message, response.status);
+  }
+};
\ No newline at end of file