Fetching all items in campaign returns 500

Hi, I have an issue with this request:

GET https://backstage.taboola.com/backstage/api/1.0/sph-beritaharian-sc/campaigns/8515428/items

it return the following error:

{
    "http_status": 500,
    "message": "Unknown server error occurred",
    "message_code": "api.action.unknown_server_error"
}

I have tried out just listing all campaigns for this account id and that works. I have also tried getting only that single campaign with id 8515428, that works as well. Getting items for campaign id 8515428 does not work.

I have tried the same to get items with the rest of campaign ids and it works for others, it just returns 500 for this one specific campaign id.

Can you please advise how to overcome this issue?