Powershell & API: Doing a Mutation Query with column Values

I am using Powershell to generate a create a new item to a Existing sheet. The code I have generated that is being submittted, is generating the following error.

StatusCode : 200
StatusDescription : OK
Content : {“errors”:[{“message”:“Variable brand of type String! was provided invalid
value”,“locations”:[{“line”:1,“column”:10}],“value”:null,“problems”:[{“path”:,“explanation”:“Expected value to not be null”…
RawContent : HTTP/1.1 200 OK

the code is as follows. (I have redacted some to protect the Innocent :smiley: )
{
" variables": {
“cols”: {
“prelim_die_lines_actual”: {
“date”: “2019-11-27”
},
“person”: “J J L”,
“date5”: {
“date”: “2019-11-22”
},
“date60”: {
“date”: “2020-01-12”
},
“products_actual”: {
“date”: “2019-10-10”
},
“date2”: {
“date”: “2019-11-22”
},
“job__”: “63344”,
“pog_approva_actual”: {
“date”: “2019-11-07”
},
“date8”: {
“date”: “2019-12-30”
},
“date52”: {
“date”: “2019-12-19”
},
“pog_submission_actual”: {
“date”: “2019-11-05”
},
“date1”: {
“date”: “2019-11-22”
},
“set_date”: {
“date”: “2020-04-16”
},
“date35”: {
“date”: “2020-03-16”
},
“date67”: {
“date”: “2019-12-09”
},
“date51”: {
“date”: “2019-11-22”
},
“brief_actual”: {
“date”: “2019-10-10”
},
“date17”: {
“date”: “2020-01-31”
},
“cost_letter_actual”: {
“date”: “2019-11-28”
},
“pp_submittal_actual”: {
“date”: “2019-11-27”
},
“date6”: {
“date”: “2019-12-02”
},
“date4”: {
“date”: “2019-12-15”
},
“date42”: {
“date”: “2020-02-06”
}
},
“brand”: "U D "
},
“query”: “mutation($brand:String!,$cols:JSON!){create_item (board_id:298028165,item_name:$brand,column_values: $cols){id}}”
}

No one has any idea?