Send OTP codes that actually arrive

• Type numbers the way your users do. Local numbers such as 0803... work as typed.
• Offer a Resend button, but only after a short wait. People who tap it five times get five codes and confuse themselves.
• Tell the user which number you sent to, so a typo is obvious.
• Some networks are slower at busy times. Give the code a few minutes to be valid.
• Limit attempts. After a few wrong codes, ask for a new one.
• Offer an alternative such as the code on WhatsApp for people whose SMS is delayed.

You are billed for each code sent, not for each check. A failed delivery is refunded.