Here's what ChatGPT said:
Hey Daniel,
The delta: 0 you're seeing is actually a good sign; it means that the OTP validation was successful. In TOTP (Time-Based One-Time Password) systems, the delta is the difference between the counter value on the server and the counter value from the OTP token. In your case, a delta of 0 indicates that both are perfectly in sync, meaning validation success.
Now, let's talk "clock drift," as Kent suggested. Clock drift happens when the clocks between the server and client (often your phone or other device) start to drift apart over time. TOTP algorithms usually accommodate for some level of clock drift by validating tokens that are a few time steps away from the current time step. So, you could see a non-zero delta value, and that would also signify a successful validation as long as it's within an acceptable range.
Hope that clears things up!