nextauthjs/next-auth · error

[createSession] Failed to fetch created session

Error message

[createSession] Failed to fetch created session

What it means

The Firebase adapter's createSession adds a session document, then reads it back via ref.get(). If the resulting data is falsy it throws '[createSession] Failed to fetch created session'. The adapter insists on returning a fully materialized session, so a failed round-trip aborts sign-in.

Solutions

1. Check Firestore security rules allow reading documents the adapter just created in the sessions collection.
2. Log sessionInit and verify the mapper produces non-empty fields before add().
3. Confirm the adapter's Firestore instance points at the same project/database as the write.
4. If a trigger cleans up session docs on create, remove or scope it.

Example fix

// before
const ref = await C.sessions.add(sessionInit)
const session = await ref.get().then((doc) => doc.data())
if (session) return session ?? null
throw new Error('[createSession] Failed to fetch created session')
// after
const ref = await C.sessions.add(sessionInit)
const snap = await ref.get()
if (!snap.exists) throw new Error('[createSession] Failed to fetch created session')
return { ...sessionInit, ...snap.data() }

function hasSessionData(d: Record<string, unknown> | undefined): d is Record<string, unknown> {
  return !!d && Object.keys(d).length > 0
}

try {
  const session = await adapter.createSession(sessionInit)
  return session
} catch (e) {
  if ((e as Error).message.includes('Failed to fetch created session')) {
    console.error('Session create/read round-trip failed; check Firestore rules on sessions', e)
    throw e
  }
  throw e
}

When it happens

Trigger: C.sessions.add(sessionInit) succeeds but the immediate get() returns empty data — security rules denying the read, sessionInit producing a doc with no fields, or a custom get/then helper failing to unwrap doc.data().

Common situations: Firestore rules that allow create but not read on the sessions collection (common with least-privilege configs); emulator/prod project mismatch; session payload mappers dropping all fields so data() comes back empty.

Understand the failure class

Background: Record Not Found Errors: "not found", RecordNotFound, and "was not found" — what they mean and how to fix them — this error's family across 28 libraries.

Related errors

• [createUser] Failed to fetch created user
• [updateUser] Failed to fetch updated user
• [updateSession] Failed to fetch updated session
• Authenticator not found.
• Authenticator not found.

AI-assisted analysis of nextauthjs/next-auth@a1a16a5a77 (2026-08-28). Data as JSON: /api/errors/4d7d7b8d330613e4. Report an issue: GitHub.

Appendix: source

Thrown at packages/adapter-firebase/src/index.ts:178

      return account ?? null
    },

    async unlinkAccount({ provider, providerAccountId }) {
      await deleteDocs(
        C.accounts
          .where("provider", "==", provider)
          .where(mapper.toDb("providerAccountId"), "==", providerAccountId)
          .limit(1)
      )
    },

    async createSession(sessionInit) {
      const ref = await C.sessions.add(sessionInit)
      const session = await ref.get().then((doc) => doc.data())

      if (session) return session ?? null

      throw new Error("[createSession] Failed to fetch created session")
    },

    async getSessionAndUser(sessionToken) {
      const session = await getOneDoc(
        C.sessions.where(mapper.toDb("sessionToken"), "==", sessionToken)
      )
      if (!session) return null

      const user = await getDoc(C.users.doc(session.userId))
      if (!user) return null

      return { session, user }
    },

    async updateSession(partialSession) {
      const sessionId = await db.runTransaction(async (transaction) => {
        const sessionSnapshot = (
          await transaction.get(

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