Blog
Push, OTP and sign-in, explained for developers
Fixes for the problems developers search for most: FCM delivery, battery savers, OTP costs and DLT, Supabase and Firebase limits, passkeys and push approval.
Push notifications
8 min readMigrating from the FCM legacy API to HTTP v1The FCM legacy API is shut down. How to move to HTTP v1: service account tokens, the new payload, sending to many tokens, and Node, PHP and cURL examples.8 min readFCM says success but the notification never arrivesWhy Android does not show FCM notifications when the app is closed or killed: message types, priority, Doze, permissions, stale tokens and OEM battery savers.7 min readWhy push notifications go missing on Xiaomi, Oppo, Vivo and RealmeBattery savers on Xiaomi, Redmi, Poco, Oppo, Realme, Vivo and OnePlus stop apps and drop pushes. What developers can change in the app and what users must switch on.5 min readIs Firebase push notification free or paid?Firebase Cloud Messaging is free on every plan. What the limits are, what is not free around it, and what a push backend costs to run.7 min readSending push notifications from a Node.js serverSend FCM push notifications from Node.js: firebase-admin setup, one user, many tokens, topics, all users, scheduling and cleaning up dead tokens.6 min readExpo push notifications work in development but not in the APKThe common reasons Expo push notifications stop in production builds: FCM v1 credentials, google-services.json, Expo Go limits, receipts and Android channels.
OTP and email
7 min readWhat an SMS OTP costs in India, and what DLT asks of youSMS OTP prices in India per message, what DLT registration involves for OTP templates, whether you can send OTP without DLT, and the cheaper options.5 min readSupabase "email rate limit exceeded": the fixSupabase's built-in email sender is for testing and allows only a few emails an hour. How custom SMTP raises the limit, and other ways to send sign-in codes.6 min readEmail OTP in Better Auth, end to endSet up the Better Auth email OTP plugin, choose a sender for the codes, and handle expiry, tries and rate limits in production.6 min readFirebase Auth has no email OTP. Here is how to add oneFirebase Auth offers email links, not 6-digit email codes. How to build email OTP sign-in with a Cloud Function and a custom token.6 min readEmail OTP or SMS OTP?Email OTP and SMS OTP compared on price in India, DLT, delivery, SIM swap and phishing risk, with when to use each.
Push authentication
6 min readPush authentication, MFA fatigue and number matchingWhat push authentication is, how MFA fatigue attacks beat it, why number matching stops them, and how it compares with an OTP.6 min readThe RBI's 2025 authentication directions, for developersWhat the RBI's Authentication Mechanisms for Digital Payment Transactions Directions, 2025 ask of apps from 1 April 2026, and the alternatives to SMS OTP they name.
Comparisons
CompareA OneSignal alternative, now that free mobile push stops at 1,000 usersOneSignal's free plan now stops mobile push at 1,000 monthly users. What it costs to stay, the free alternatives, and how SignOps compares in rupees.CompareOTP service providers in India, compared on price and setupSMS, WhatsApp, email and push OTP providers in India with prices per code, DLT rules, and the options that need no DLT registration.CompareAn MSG91 alternative for apps that want more than SMSWhat MSG91 charges for SMS and email OTP, where it is the right choice, and when SignOps push, approvals and passkeys cost less.CompareA Twilio Verify alternative, priced in rupeesTwilio Verify charges $0.05 a push verification plus SMS. What that costs in India, and how SignOps Approve and email OTP compare.CompareFree push notification services for Android, iOS and the webEvery free push notification option in 2026, what the free tier covers, and what you still have to build: FCM, Expo, OneSignal, Pusher, Truepush and SignOps.
Send your first push today.
Free for 1,000 push devices, 100 approvals a day, 10,000 passkey sign-ins a month and 500 email codes to try. No card until you pass a free amount.