[SalesForce] Delete multiple records using REST Api

It looks like you have a placeholder/sample shortcode; assuming you are swapping this out when making the call, if this is a new shortcode that has not completed carrier review, it is likely the STOP keyword is not configured in the UI.

You can definitely use workbench to execute these

Use the below for the request

/services/data/v34.0/composite/tree/Account

and in the body use the below JSON

{
"records" :[{
"attributes" : {"type" : "Account", "referenceId" : "ref1"},
"name" : "SampleAccount1",
"phone" : "1111111111",
"website" : "www.salesforce1.com",
"numberOfEmployees" : "100",
"industry" : "Banking"   
},{
"attributes" : {"type" : "Account", "referenceId" : "ref2"},
"name" : "SampleAccount2",
"phone" : "2222222222",
"website" : "www.salesforce2.com",
"numberOfEmployees" : "250",
"industry" : "Banking"
},{
"attributes" : {"type" : "Account", "referenceId" : "ref3"},
"name" : "SampleAccount3",
"phone" : "3333333333",
"website" : "www.salesforce3.com",
"numberOfEmployees" : "52000",
"industry" : "Banking"
},{
 "attributes" : {"type" : "Account", "referenceId" : "ref4"},
 "name" : "SampleAccount4",
 "phone" : "4444444444",
 "website" : "www.salesforce4.com",
 "numberOfEmployees" : "2500",
 "industry" : "Banking"
  }]
}

You should see the response in workbench

Alternatively you can use POSTMAN to experiment with this API .

You will need to create a connected app in salesforce and use oauth 2.0 to get access token for subsequent calls

use the below link for reference