Error 400 (Bad Request) on edit issue API

Hello! I’m currently building an app that needs to automatically update a custom field on Jira. I’m trying to use the edit issue API, but I keep getting error 400 - Bad Request. Maybe someone here can help?

Here’s my request:

    "method": "PUT",
    "headers": {
        "Accept": "application/json",
        "Content-Type": "application/json"
    "body": {
        "fields": {
            "customfield_10068": "2000-01-01T00:00:00+00:00"

The error message just says that my request is invalid and that I should read the API, but I’m not sure exactly what I should be doing instead.

Any help is appreciated!