many apologies
i've looked at the code and the only thing i can think of left is that your computer might be blocking https://worldtimeapi.org/ from being called by unity to verify the date.
i can see there are a big chunk of people coming across this error.
i will continue to think of solutions but please let me know if either of these help:
1 - make sure you're not on a Corporate/school network.
2 - make sure you do not have parental controls or content filters enabled.
if all else fails, it is possible that the api is rate limiting requests. meaning you may have to wait until other people playing the game slow down their network verifications.