I have found that some users have such issue, including new users and very early users, and all other users are normal.
I first integrated zendesk about 2 years ago, and the zendesk payload data structure created at that time was:

const payload = {
user_id: dbUser. user_id,
external_id: dbUser. user_id,
name: `xxx`,
email: dbUser. email,
jti: uuidv4(),
}

Among them, name/email/jti complies with zendesk doc rules. Until recently, after discovering this issue, I rechecked Zendesk doc, added the missing iat field, and retested, and found that the problem still exists.

After there was no effective solution, I found the email of the user in question fromzendesk admin dashboard > people > bulk action > delete end usersand deleted it, then used this email to test successfully create a ticket.

If an individual user has such a problem, I can do this, but it is very difficult when there is too much data.

The following is the zendesk jwt token payload info created by the two accounts respectively. After passing in the zendesk jwt token, one can create a ticket normally, and the other cannot. I checked the created payload and it looks like they have fields/values as per the docs

// Unusable token payload:
{
"user_id": "fdf531c9-a537-400a-9e3a-9f4c249bea33",
:“external_id fdf531c9-a537-400a-9e3a-9f4c249bea33",
"name": "my name",
"email": "myemail@****.com",
"jti": "dea51c68-7f69-481a-8404-98b481aaacad",
"iat": 1686032439,
"version": 1,
"type": 2,
"epoch": 1686032439691,
"channel_id": "xxxx",
"exp": 1689920439
}

// Available token payload:
{
"user_id": "04133dd1-634a-436a-af8a-c196c54c2f50",
"external_id": "04133dd1-634a-436a-af8a-c196c54c2f50",
"name": "Other Name",
"email": "otheremail@****.com",
"jti": "47056eac-7156-43e6-b395-045d85a45f7e",
"iat": 1686032750,
"version": 1,
"type": 2,
"epoch": 1686032750863,
"channel_id": "xxxx",
"exp": 1689920750
}