![\"Four](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/why-otp-fails.png\")
Every failed OTP is a failed login, a failed signup, or an abandoned order. Most businesses never see it happen, because the user simply leaves.<\/p>\n
What Smart OTP does differently<\/h2>\n
Smart OTP is the OTP engine inside Fast2SMS. You create one OTP template and choose a primary channel, SMS or WhatsApp. If the primary fails, the same code fires on the other channel automatically. Nobody waits, nobody retries, nothing changes in your website code.<\/p>\n Log in to Fast2SMS<\/a> and open the Smart OTP section. Click Add OTP Template<\/strong> and pick your channel:<\/p>\n A WhatsApp OTP template uses an approved authentication template on your WhatsApp Business number. The message carries your verified business name and even a Copy code button:<\/p>\n An SMS OTP template uses your DLT-approved template, sender ID and entity:<\/p>\n Each template gets an OTP ID<\/strong>. Click Setup next to Fallback to attach the second channel. Change the channel or fallback any time in the panel, and every website using that OTP ID follows instantly, with no code changes.<\/p>\n Two endpoints do the whole job. Fast2SMS generates the code, sends it on your OTP ID’s channel, and checks it on verify. You never store or compare OTPs yourself. Full reference: send OTP<\/a> and verify OTP<\/a>.<\/p>\n Success response:<\/p>\n WhatsApp OTPs use authentication templates at INR 0.25 per delivered message, with automatic refunds for failures. SMS OTPs go at your DLT bulk rate. There is no monthly fee and no platform charge on top.<\/p>\n The OTP feature of Fast2SMS. One OTP template with a primary channel (SMS or WhatsApp) and an optional automatic fallback on the other channel. Your website just uses the OTP ID.<\/p>\n Many businesses now put WhatsApp first: it is cheaper at INR 0.25, carries your verified name, and failed messages are refunded. SMS as fallback catches users without WhatsApp. The reverse works too.<\/p>\n For the SMS channel, yes, TRAI requires it. Fast2SMS gives free DLT support. The WhatsApp channel needs no DLT, only a one-time Meta template approval.<\/p>\n Yes. The channel and fallback live in the OTP ID configuration at Fast2SMS. Edit them in the panel and every site using that OTP ID follows immediately.<\/p>\n OTP routes are priority routes, so codes are sent within seconds of the request. The fallback fires automatically when the primary attempt fails.<\/p>\n Yes, sensible ones. Resend works within a 10 minute window, and the WordPress plugin adds its own per-phone and per-IP rate limits with a visible cooldown timer.<\/p>\n Yes. Send yourself a real OTP from the panel, or use the end-to-end test card inside the WordPress plugin.<\/p>\n On WordPress or Shopify: paste the OTP ID into the free plugin or app. On custom sites: three REST calls. Most setups finish inside fifteen minutes.<\/p>\n Create your free account, add one OTP template with fallback, and every code your business sends gets two chances to arrive.<\/p>\n![\"Diagram](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/smart-otp-flow.png\")
Setting it up: the OTP Template List<\/h2>\n
![\"Assign](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/smart-otp-assign-template.png\")
![\"Approved](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/smart-otp-whatsapp-template.png\")
![\"Approved](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/smart-otp-sms-template.png\")
Using your OTP ID everywhere<\/h2>\n
\n
Send and verify OTPs from your own code<\/h2>\n
Send OTP with cURL<\/h3>\n
curl --request POST \\\n --url https:\/\/www.fast2sms.com\/dev\/otp\/send \\\n --header 'Authorization: YOUR_API_KEY' \\\n --header 'accept: application\/json' \\\n --header 'content-type: application\/json' \\\n --data '{\n \"otp_id\": \"11111111\",\n \"mobile\": \"8888888888\"\n }'<\/code><\/pre>\n{\n \"return\": true,\n \"status_code\": 200,\n \"request_id\": \"lwdtp7cjyqxvfe9\",\n \"message\": \"OTP sent successfully\"\n}<\/code><\/pre>\nVerify OTP with cURL<\/h3>\n
curl --request POST \\\n --url https:\/\/www.fast2sms.com\/dev\/otp\/verify \\\n --header 'Authorization: YOUR_API_KEY' \\\n --header 'accept: application\/json' \\\n --header 'content-type: application\/json' \\\n --data '{\n \"mobile\": \"8888888888\",\n \"otp\": \"123456\"\n }'<\/code><\/pre>\n{\n \"return\": true,\n \"status_code\": 200,\n \"message\": \"OTP verified successfully\"\n}<\/code><\/pre>\nThe same flow in PHP<\/h3>\n
<?php\n\/\/ 1. Send the OTP\n$ch = curl_init('https:\/\/www.fast2sms.com\/dev\/otp\/send');\ncurl_setopt_array($ch, array(\n CURLOPT_RETURNTRANSFER => true,\n CURLOPT_POST => true,\n CURLOPT_HTTPHEADER => array(\n 'Authorization: YOUR_API_KEY',\n 'Content-Type: application\/json',\n 'Accept: application\/json',\n ),\n CURLOPT_POSTFIELDS => json_encode(array(\n 'otp_id' => '11111111',\n 'mobile' => '8888888888',\n )),\n));\n$send = json_decode(curl_exec($ch), true);\ncurl_close($ch);\n\nif (!empty($send['return'])) {\n \/\/ Sent. Keep $send['request_id'] for tracing.\n}\n\n\/\/ 2. Verify the code the user typed\n$ch = curl_init('https:\/\/www.fast2sms.com\/dev\/otp\/verify');\ncurl_setopt_array($ch, array(\n CURLOPT_RETURNTRANSFER => true,\n CURLOPT_POST => true,\n CURLOPT_HTTPHEADER => array(\n 'Authorization: YOUR_API_KEY',\n 'Content-Type: application\/json',\n 'Accept: application\/json',\n ),\n CURLOPT_POSTFIELDS => json_encode(array(\n 'mobile' => '8888888888',\n 'otp' => $_POST['otp'], \/\/ the code the user entered\n )),\n));\n$verify = json_decode(curl_exec($ch), true);\ncurl_close($ch);\n\nif (!empty($verify['return'])) {\n \/\/ Verified. Log the user in or confirm the order.\n} else {\n \/\/ Wrong or expired code: $verify['message']\n}<\/code><\/pre>\nErrors you should handle<\/h3>\n
\n
400 Invalid OTP ID<\/code> on send: the otp_id does not exist in your panel. Copy it from the OTP Template List.<\/li>\n401 Invalid Authorization key<\/code>: wrong or revoked API key.<\/li>\n400 Invalid OTP<\/code> on verify: the user typed the wrong code. Let them retry or resend.<\/li>\n404 OTP not found or already verified<\/code>: each code verifies once. Ask for a fresh OTP.<\/li>\n<\/ul>\nWhat OTPs cost<\/h2>\n
![\"WhatsApp](\"https:\/\/www.fast2sms.com\/help\/wp-content\/uploads\/2026\/07\/otp-price-chart.png\")
Frequently asked questions<\/h2>\n
What is Smart OTP?<\/h3>\n
Which channel should be primary?<\/h3>\n
Do I need DLT registration for OTP SMS?<\/h3>\n
Can I change the channel later without touching my website?<\/h3>\n
How fast do OTPs arrive?<\/h3>\n
Is there a resend limit?<\/h3>\n
Can I test before going live?<\/h3>\n
What does integration take?<\/h3>\n
Stop losing logins to lost OTPs<\/h2>\n