Serialization of 'Illuminate\Http\UploadedFile' is not allowed

Before the Offer::create if you can try and dump what does your imgNames contains?

using dd($imgNames) and make sure that each of the items of the array is just the name of the image and not an instance of UploadedFile, as that's where it seems to go wrong.

You are trying to redirect with input.

This is not possible since your input contains files.

Redirects are always a GET request so anything that you might pass to that route would need to be converted to url query string parameters.

@snapey Thats it! I change my redirect with input (and little validation code)

public function store(Request $request)
    {
        // validation
        $validator = Validator::make($request->all(), [
            'title' => 'required|min:4|max:128',
            'description' => 'required|min:16',
            'min_price' => 'required|numeric',
            'date_end' => 'required',
            'img' => 'required|max:10000'
        ]);
        // clear inputs
        $title = e($request->title);
        $description = e($request->description);
        $min_price = e($request->min_price);
        $date_end = e($request->date_end);
        // redirect if fails
        if ($validator->fails()) {
            return redirect('/offers/create')->withInput(
                [
                    'title' => $request->title, 
                    'description' => $request->description, 
                    'min_price' => $request->min_price, 
                    'date_end' => $request->date_end
                    ]
                )->withErrors($validator);
        }
        // url
        $urlExists = true;
        $i = 1;
        while ($urlExists) {
            $url = Str::slug($title . '-' . Str::random(8), '-');
            $checkUrlExists = Offer::where('url', $url)->count();
            $i++;
            if ($checkUrlExists == 0) {
                $urlExists = false;
            }
        }
        // imgs
        $imgNames = [];
        if ($imgs = $request->file('img')) {
            $i = 1;
            foreach ($imgs as $img) {
                $name = time() . '-' . $i . '.' . $img->getClientOriginalExtension();
                $img->move(storage_path('app/public/images/offers'), $name);
                array_push($imgNames, $name);
                $i++;
            }
        }
        // store
        Offer::create([
            'user_id' => auth()->user()->id,
            'title' => $title,
            'description' => $description,
            'url' => $url,
            'min_price' => $min_price,
            'date_end' => $date_end,
            'img' => serialize($imgNames)
        ]);
        // redirect
        return redirect('/offers')->with('success', 'Success!');
    }

and its working! Thanks all for help. Greetings all.