Sharethrough user sync endpoint returns 422 Unprocessable Content

[modessef1]

Hi, I'm seeing a persistent `422 (Unprocessable Content)` error on my website when Prebid triggers the Sharethrough user sync pixel (as shown in the attached screenshot).

The failing request goes to:
https://match.sharethrough.com/FGmRCMMc/v1?...

Could you help me look into this and advise on how to fix it? Is this an issue with my Prebid.js implementation/configuration, or is it a bug on the endpoint side?

Thanks!