Call to retrieve data for one specific person returns 403 Forbidden

I have used this API for a long time to get certain field values like this:

https://api.icims.com/customers//people/?fields=field14636,field24261,workexperience,field23767,firstname,lastname,email

It has always worked in the past, but now there is one personID in our system that always returns this response:

{
"errors": [
{
"errorMessage": "Person is not accessible.",
"errorCode": 3
}
]
}

All of the other people can still be retrieved successfully. What can I do about this?

Thanks.