Generate php image

I am having trouble generating an image from PHP. My problem is that the file is generated perfectly with the structure I need, but when I open the image file I get the following message: "It seems that the format of this file is not supported." I am doing it with Laravel

I enclose code of how I generate the image and save it in the DB (the name of the image)

HTML:

<div class="col-md-5">
    <div class="card-header">Firma</div>
    <input type="color" class="js-color-picker  color-picker">
    <input type="range" class="js-line-range" min="1" max="72" value="1">
    <label class="js-range-value">1</label>Px
    <canvas class="js-paint paint-canvas" id="canvas" name="firma" width="400" height="300"></canvas>
    <input type="hidden" name="_token" id="token" value="{{ csrf_token() }}">
</div>

Controller:

public function crearPaciente(Request $request){

    $nombre = $request->get('nombre');
    $apellidos = $request->get('apellidos');
    $dni = $request->get('dni');
    $fechaNacimiento = $request->get('fechaNacimiento');
    $lugarNacimiento = $request->get('lugarNacimiento');
    $direccion = $request->get('direccion');
    $codigoPostal = $request->get('codigoPostal');

    $telefonoFijo = $request->get('telefonoFijo');
    $telefonoMovil = $request->get('telefonoMovil');
    $compania = $request->get('compania');

    

    //obtenemos la fecha de firma
    $fecha = \Carbon\Carbon::now();
    $fechaFinal = $fecha->toDateString();

    $firma = $request->get('dataURL');

    $this->generateImage($firma, $nombre, $apellidos);

    $pacienteFirma = $nombre.$apellidos.".png";

    $guardarFirma = str_replace(' ', '', $pacienteFirma);

    
    $data = array('nombre'=>$nombre,
                  "apellidos"=>$apellidos,
                  "dni"=>$dni,
                  "fecha_nacimiento"=>$fechaNacimiento,
                  "lugar_nacimiento"=>$lugarNacimiento,
                  "direccion"=>$direccion,
                  "cod_postal"=>$codigoPostal,
                  "tlf1"=>$telefonoFijo,
                  "tlf2"=>$telefonoMovil,
                  "compania"=>$compania,
                  );

    $consentimiento = array('fechaFirma' => $fechaFinal,
                            'firma' => $guardarFirma
                           );


    \DB::table('pacientes')->insert($data);
    \DB::table('lopds')->insert($consentimiento);

I capture the resquest of the canvas

$firma = $request->get('dataURL');

$this->generateImage($firma, $nombre, $apellidos);

function "generateImage"

public function generateImage($img, $nombre, $apellidos){

    $cadenaNombre = $nombre.$apellidos;
    
    $nombreApellidos = str_replace(' ', '', $cadenaNombre);

    $path = "images/".$nombreApellidos.".png";
    
    $imgTran1 = str_replace('data:image/png;base64,', '', $img);
    $imgTran2 = str_replace(' ', '+', $img);
    $data = base64_decode($imgTran2);

    $success = file_put_contents($path, $data);
}

I have to say, that before transforming the image, the resulting canvas string is a base64 string, as you can see in the $imgTran1 variable.

Thanks in advance for the help, since I don't know what could be wrong so that the image is not displayed. When returning it in html again, it doesn't show either.

cheers and thank you again