unopim/unopim

use Closure;
use Illuminate\Contracts\Validation\ValidationRule;

class SeparatorTypes implements ValidationRule
{
    const SEPERATOR_TYPES = [
        ',',
        ';',
        '|',
    ];

    public function validate(string $attribute, mixed $value, Closure $fail): void
    {
        if (! in_array($value, self::SEPERATOR_TYPES)) {
            $fail('core::validation.seperator-not-supported')->translate();
        }
    }
}

use Webkul\DataTransfer\Rules\SeparatorTypes;

class ExportController extends Controller
{
    // ...

    public function store()
    {
        $exporters = array_keys(config('exporters'));

        $this->validate(request(), [
            'code'                => 'required|unique:job_instances,code',
            'entity_type'         => 'required|in:'.implode(',', $exporters),
            'filters'             => 'array',
            'filters.file_format' => 'required',
            'field_separator'     => ['required_if:filters.file_format,Csv', new SeparatorTypes],
        ]);

        // ...
    }

    // ...
}