FormRequest: Check if coupon code still within validity date using exists validation

Hello there,

I want to validate a coupon code. The database table looks like this:

        Schema::create('coupons', function (Blueprint $table) {
            $table->increments('id');
            $table->text('code');
            $table->date('valid_from');
            $table->date('valid_until');
            $table->text('discount_mrc');
            $table->text('discount_otc');
            $table->timestamps();
        });

Now in my FormRequest validation I would like to check whether the provided coupon code exists in the database AND whether it is still valid, meaning whether it is within the valid_from to valid_until range.

I tried to limit it to the valid_until range first but even this I cannot do:

'coupon_code'=>'exists:coupons,code,valid_until,>=NOW()',

Any idea whether this works with the "exists" validation out of the box or whether I would have to create a custom validation?

Thanks Andreas