fix(recurring-invoices): scale scheduled generation

app/Http/Requests/RecurringInvoiceFrequencyRequest.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Http\Requests;
+
+use App\Rules\ValidCronExpression;
+use Illuminate\Contracts\Validation\ValidationRule;
+use Illuminate\Foundation\Http\FormRequest;
+
+class RecurringInvoiceFrequencyRequest extends FormRequest
+{
+    /**
+     * Determine if the user is authorized to make this request.
+     */
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * Get the validation rules that apply to the request.
+     *
+     * @return array<string, ValidationRule|array<mixed>|string>
+     */
+    public function rules(): array
+    {
+        return [
+            'frequency' => ['required', 'string', new ValidCronExpression],
+            'starts_at' => ['required', 'date'],
+        ];
+    }
+}