Recently started getting timestamp_signup error when adding a member

Recently I’ve started getting a “This value is not a valid datetime.” error saying the timestamp_signup is not a valid datetime. This is in C# code that hasn’t changed in over a year:

`var member = new Member { EmailAddress = email, StatusIfNew = Status.Subscribed, EmailType = “html”, IpOpt = userIPAddress, TimestampSignup = DateTime.UtcNow.ToString(“s”) };

var result = await mailChimpManager.Members.AddOrUpdateAsync(_ListId, member);`

I’ve tried a dozen variations of sending a datetime and continue to get the same error.

[m-reinke]

Had the same. Changed timestamp format to: member.TimestampSignup = DateTime.UtcNow.ToString(“yyyy-MM-dd hh:mm:ss”); See also StackOverflow

[ronaldbarendse]

@brandonseydel Would adding the above TimestampSignupUtc property still add value?