Looker API Error : Filters query string must be begin with

On Create Schedule API, I’m passing this filter string below in the body using Nodejs.

    "filters_string": "?Hub+Code=&Cohort+Name=SHRM&Course+Name=&Experience=Course",

When I ran the code in the Looker API Explorer, it worked perfectly, but when I ran it through VSCode or Postman, I got the below error. 

Error: 422 Processable Entity: 

   "message": "Validation Failed",
"errors": [
{
"field": "filters_string",
"code": "invalid",
"message": "Filters query string must be begin with '?'",

I tried all kinds of ways to solve it, but I failed. Please help.

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