The Response content must be a string or object implementing __toString(), "boolean" given. laravel 5.8 I don't know why I'm getting this error

If I try to make a deposit, an error keeps popping up. I use to make deposits without any error. It points to this direction:

C:\xampp\htdocs\mysystem\vendor\symfony\http-foundation\Response.php

This is the error That pops up in the browser.

public function setContent($content)
    {
        if (null !== $content && !\is_string($content) && !is_numeric($content) && !\is_callable([$content, '__toString'])) {
            throw new \UnexpectedValueException(sprintf('The Response content must be a string or object implementing __toString(), "%s" given.', \gettype($content)));
        }
 
        $this->content = (string) $content;
 
        return $this;
    }

My controller

    class DepositTransactionsController extends Controller
{
    public function createDeposit(){
        return view('agent_dashboards.add_customer_deposit');
    }

    public function saveDeposit(Request $request){
        $this->validate($request,[
            'customer_id' => 'required|exists:customers',
            'amount' => 'required'
        ]);
        
        $customer = Customer::where('customer_id',$request->input('customer_id'))->first();

        $deposit_trans = new DepositTransaction();
        $deposit_trans->customer_id = $customer->id;
        $deposit_trans->agent_id = Auth::user()->id;
        $deposit_trans->amount = $request->input('amount');
        // add sms api
        $response = $this->urlBuilder($customer->phone_number, $request->input('amount'));
        if(strpos($response, 'SUCCESS') === false){
            return $response;
        }else{
            $deposit_trans->sms_notification_status = "SENT";
            $deposit_trans->save();
        }

        $customer->total_savings = $customer->total_savings + $request->input('amount');
        $customer->save();
        
        $temp_deposit_sum_record = TemporaryDailyDeposit::where('agent',Auth::user()->firstname.' '.Auth::user()->surname)->first();
        if($temp_deposit_sum_record == null){
            $temp_deposit_sum_record = new TemporaryDailyDeposit();
            $temp_deposit_sum_record->agent = Auth::user()->firstname.' '.Auth::user()->surname;
            $temp_deposit_sum_record->total_amount_recieved = $request->input('amount');
            $temp_deposit_sum_record->save();
        }else{
            $temp_deposit_sum_record->total_amount_recieved += $request->input('amount');
            $temp_deposit_sum_record->save();
        }

        return redirect('/home');
    }

    private function urlBuilder($number, $amount){
        $username = "";
        $password = "";
        $from = "";
        $to = $this->getPhoneNumber($number);
        $message = $this->getMessage($amount);
        $baseurl = "https://isms.wigalsolutions.com/ismsweb/sendmsg/";
        $params = "username=".$username."&password=".$password."&from=".$from."&to=".$to."&message=".$message;
        //send message
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $baseurl);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS,$params);
        $response = curl_exec($ch);
        curl_close($ch);

        return $response;
    }

    private function getPhoneNumber($number){
        if(strlen($number) == 13){
            return substr($number,1);
        }else{
            return "233".substr($number,1);
        }
    }

    private function getMessage($amount){
        $message = "Dear valued customer,\n We wish to notify you that, we have recieved your deposit of GHc"
                        .number_format($amount, 2, '.', '')." into your account on this date: ".date("Y-m-d")
                        ."\n Thank you for the transaction.";
        
        return $message;
    }

    public function showDepositTransaction($id){

    }

    public function showAllDepositTransaction(){

    }
}

Here is the database table that handles transactions. I can register a user and everything works perfectly, but when a customer makes a deposit, then I get the above error.

Schema::create('deposit_transactions', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->integer('customer_id');
            $table->integer('agent_id');
            $table->double('amount');
            $table->string('sms_notification_status');
            $table->timestamps();