Error code 1867 | Office Integrator save to S3

Error code 1867 | Office Integrator save to S3

I'm trying to use the Zoho Office Integrator API to edit documents saved on an S3 buckets. I can open them all right, but when pressing "save" on the frontend, this is what I get from the POST call to https://writer.zoho.eu/writer/remotesave.im:
  1.  {
      "statuscode": 500,
      "errorCode": "1867",
      "STATUS_CODE": 500,
      "RESPONSE": "postexception"
    }
I have not found this error code in the documentation and am at a loss. If needed, I can provide code snippets.
Thank you in advance!