How to fix 422 Unprocessable Entity in httpcallout

public class Rg_TestMemberAccountCreate {
    public static void testMemberAccount(String endpoint,String token){
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint(endpoint);
        request.setMethod('POST');
        request.setHeader('Content-Type', 'application/json');
        request.setHeader('Authorization', 'Bearer '+token);
        request.setHeader('Accept', 'application/json');
        // Set the body as a JSON object
        String b = '{"data": {"attributes": {"name": "Test Rahul2","symbol": "TESTRT", "is_active": "true"},"type": "providers"}}';
        request.setBody(b);
        System.debug('Requst : '+request);
        HttpResponse response = http.send(request);
        System.debug('response: '+response);
        // Parse the JSON response
        if (response.getStatusCode() != 200) {
            System.debug('The status code returned was not expected: ' + response.getStatusCode() + ' ' + response.getStatus());
        } else {
            System.debug(response.getBody());
        }   
    }
}

do you have any idea what is wrong in my class?