JSON provided:

{
    "architecture_id": 1
}

Response:

{
  "error": {
    "message": "ERROR:  operator does not exist: character varying = integer\nLINE 1: ...architectures\".\"id\" = 1 OR \"architectures\".\"name\" = 1))  ORD...\n                                                             ^\nHINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.\n" 
  }
}

Ultimately, one should be able to provide the exact same JSON received from a GET on /api/v2/hosts/:id back as a PUT without errors.

From http://projects.theforeman.org/issues/13670

Customer is running into this.  If he typecasts it as a string there are no errors.