DateTime is getting converted into an array

[sujeet_kumar1 (Sujeet Kumar)]

When I try to save datetime in MongoDB it is getting converted into an array.
public DateTime ExpirationTime { get; set; }

Actual : ExpirationTime:Array

1. 0: 637732644002093041
2. 1:0
   Expected : 2021-11-23T11:06:23.716+00:00. Please help on this.
   Thanks,