VerifyTotp fails even when using correct otpCode

We are using TOTP for email-based OTP verification, where the OTP is generated server-side, sent via email, and typically entered by the user within ~2 minutes.

Verification code:

var keyBytes = Base32Encoding.ToBytes(otpKey);
var totp = new Totp(keyBytes, step: 120);
var isValid = totp.VerifyTotp(otpCode, out var timeStepMatched, VerificationWindow.RfcSpecifiedNetworkDelay);
return isValid;

We observe that verification works when the OTP is entered immediately, but often returns false when the same correct OTP is entered after a short delay (sometimes well under 2 minutes).

We expected the OTP to remain valid for approximately the full 120 seconds from the moment it is generated, but this does not seem to be the case. We would appreciate clarification on whether this usage pattern is supported or if a different approach is recommended.

Start with the Totp.VerifyTotp entry point and the shown step: 120 and VerificationWindow.RfcSpecifiedNetworkDelay arguments. Clarify how validity is measured and whether server-generated email codes are supported as described; document the expected behavior or recommended approach when the answer is established.