trigger LeadCallout on Lead (after insert) {
For (Lead l: Trigger.new){
    PostLeadtoBP.makePostLeadtoBP(l.Id, l.Phone);
}

public class PostLeadtoBP {
public static void makePostLeadtoBP(String leadId, String phoneNo){
    Http http = new Http();
    HttpRequest req = new HttpRequest();
        long unixTime = System.currentTimeMillis() / 1000L;
    HttpResponse res = new HttpResponse();
    req.setEndpoint('/clientweb/api/v1/chats?tenantUrl=sprout.brightpattern.com&timestamp='+unixTime);
    req.setMethod('POST');
    // Set Header for the Authorization
    req.setHeader('Content-Type', 'application/json;charset=UTF-8');
    req.setHeader('Authorization', '********************* appId="*********************", clientId="WebChat"' );
    // Set the body as a JSON object
    req.setBody(',parameters: {LeadID='+EncodingUtil.urlEncode(leadId,'UTF-8')+'phone='+EncodingUtil.urlEncode(phoneNo,'UTF-8') );
    req.setCompressed(true); // otherwise we hit a limit of 32000
     try {
        res = http.send(req);
    } catch(System.CalloutException e) {
        System.debug('Callout error: '+ e);
        System.debug(res.toString());
    }
}