Configuration API not working

Summary:

We have tried to use configuration API. But we are getting below error.

Basically in our implmentation there is array set and we are setting data using in configuration API.

End Point -

1. https://bigmachines.com/rest/v9/configsITA.sITAProductLine.sITAModel/actions/_configure

Payload

{
"cacheInstanceId": "-1",
"bsId": 3455345,
"documentId": 345345,
"configData": {
"_setsITAConnectedArraySet": {
"items": [
{
"_index": 0,
"country": {
"value": "United States",
"displayValue": "United States"
},
"countryCode": {
"value": "US",
"displayValue": "US"
},
"iATACode": "COA",
"iMAC": {
"value": "Existing",
"displayValue": "Existing"
},
"serviceID": "A-60-PBLR645-129636",
"notes": "",
"cPQ_Site_Id": "CPQ-81792_0003",
"eligibleForOrdering": "NO",
"bOSSOrderReference": "N-60-142280",
"serviceDescription": "64 kbps",
"previousServiceMRC": "3000.00",
"siteIdentifier": "Test Site",
"townAirport": {
"value": "Town",
"displayValue": "Town"
},
"routerNameConnectionID": "PBLR645",
"iSP": {