I am able to access the API from Postman successfully.
When attempting to make the same call from ServiceNow I get a 401 error.

Code
Code to generate header in ServiceNow:

getSimpleScreeningRequestAuthHeader : function(dateSent,payload){
        var contentLength = unescape(encodeURIComponent(payload)).length,
            environment = {
                "gateway-url": gs.getProperty('x_525112_refinitiv.refinitiv.gateway_url'),
                "gateway-host": gs.getProperty('x_525112_refinitiv.refinitiv.gateway_host'),
                "content": "application/json",
                "api-key": gs.getProperty('x_525112_refinitiv.refinitiv.api_key')
            },
            dataToHash = "(request-target): post " + environment["gateway-url"] + "cases/screeningRequest\n" +
                "host: " + environment["gateway-host"] + "\n" +
                "date: " + dateSent + "\n" +
                "content-type: " + environment["content"] + "\n" +
                "content-length: " + contentLength + "\n" +
                payload,
            hmac = this._generateHash(dataToHash),
            authHeader = "Signature keyId=\"" + environment["api-key"] + "\",algorithm=\"hmac-sha256\",headers=\"(request-target) host date content-type content-length\",signature=\"" + hmac + "\"";
        var debug = {
            "environmet": environment,
            "dataToHash": dataToHash,
            "hmac": hmac
        };
        gs.info('test this - script include debug: ' +JSON.stringify(debug));
        
        return authHeader;
    },
    
    _generateHash : function(dataToHash){
        var hmacUtil = new x_525112_cryptojs.CryptoJS_Wrapper(),
            secret = gs.getProperty('x_525112_refinitiv.refinitiv.api_secret'),
            hash = hmacUtil.HmacSHA256(dataToHash, secret);
        return hmacUtil.convertToBase64(hash);
        //return gs.base64Encode(hash)
    }

**payload is the body of the REST message

Code to make the call

var dateToday  = new Date().toGMTString(),
    restBody = {
    "groupId": "****", (group id removed for security, have verified it matches Postman)
    "entityType": "UNSPECIFIED",
    "caseId": "",
    "providerTypes": [
        "WATCHLIST"
    ],
    "caseScreeningState": {
        "WATCHLIST": "INITIAL"
    },
    "name": "John Smith",
    "nameTransposition": false,
    "secondaryFields": [],
    "customFields": []
},
    authHeaderString = new x_525112_refinitiv.refinitivWCUtils().getSimpleScreeningRequestAuthHeader(dateToday,JSON.stringify(restBody));

try { 
    var endPoint = gs.getProperty('x_525112_refinitiv.refinitiv.gateway_host') + gs.getProperty('x_525112_refinitiv.refinitiv.gateway_url'),
    contentLength = unescape(encodeURIComponent(restBody)).length,
    r = new sn_ws.RESTMessageV2('x_525112_refinitiv.refinitiv_world_check', 'SEQ-screen-sync-simple');
    r.setStringParameterNoEscape('authorizarionString', authHeaderString);
    r.setStringParameterNoEscape('currentDate', dateToday);
    r.setStringParameterNoEscape('endPoint', endPoint);
    r.setStringParameterNoEscape('contentLength', contentLength);
    r.setStringParameter('payload', restBody);

    var response = r.execute();
    var responseBody = response.getBody();
    var httpStatus = response.getStatusCode();

    var debug = {
        "date": dateToday,
        "endPoint": endPoint,
        "httpStatus": httpStatus
    }
    gs.print(JSON.stringify(debug));
    gs.print('authHeaderString is: ' + authHeaderString);
    
}
catch(ex) {
    var message = ex.message;
    gs.print('error caught, message: ' + message);
}

Debug & gs.print information returned after making the REST call

var scriptIncludeDebug= {
    "environmet": {
      "gateway-url": "/v2/",
      "gateway-host": "api-worldcheck.refinitiv.com",
      "content": "application/json",
      "api-key": "*****" (key removed for security, have verified it matches Postman)
    },
    "dataToHash": "(request-target): post /v2/cases/screeningRequest\nhost: api-worldcheck.refinitiv.com\ndate: Fri, 18 Mar 2022 14:57:35 GMT\ncontent-type: application/json\ncontent-length: 238\n{\"groupId\":\"******\",\"entityType\":\"UNSPECIFIED\",\"caseId\":\"\",\"providorTypes\":[\"WACHTLIST\"],\"caseScreeningState\":{\"WATCHLIST\":\"INITIAL\"},\"name\":\"John Smith\",\"nameTransposition\":false,\"secondaryFields\":[],\"customFields\":[]}", (group id removed for security, have verified it matches Postman)
    "hmac": "6kVaZfQIuChZ2dldnrHrrYv9McZOPjSMRdAXvZhAlzw="
},
bgScriptDebug = {
    "date": "Fri, 18 Mar 2022 14:57:35 GMT",
    "endPoint": "api-worldcheck.refinitiv.com/v2/",
    "httpStatus": 401
}

(keyID removed for security, have verified it matches Postman and in both Signatures)
var SNC = ' Signature keyId="******",algorithm="hmac-sha256",headers="(request-target) host date content-type content-length",signature="6kVaZfQIuChZ2dldnrHrrYv9McZOPjSMRdAXvZhAlzw=" '
var PMN = ' Signature keyId="******",algorithm="hmac-sha256",headers="(request-target) host date content-type content-length",signature="M8CoTayADFfsJFU8kL1MO5FGv/kmLPedsh/E+rRHbc8=" '

I have verified the server date/time is within 30 seconds of https://time.is

Any help you can offer would be greatly appreciated.