I am not sure but If I face this issue how I will debug it, follow the steps I hope the issue will resolved.
enable debugging from .env
APP_DEBUG=true
and then check the error, if it has already enabled then remove all content from blade file just add one
<h1>Hello this is for testing purpose</h1>
then try and replace
return $pdf->download('kwitansi-' . $request->no_kwitansi . '.pdf');
with
return $pdf->download('test.pdf');