You can test the widget on a free plan. It can be visited by 100 customers for entire period of the widget usage (not monthly). Only actual widget visitors are counted, not all visitors of the site. A single customer who visits the widget 1000 times, is considered as 1 visitor.
This should be enough for about 2 weeks of testing in case when the widget traffic is low. To remove this restriction, upgrade your subscription plan.
If all 100 users of the free plan are used up, new customers will not be able to open the widget. They will see these messages:
Those customers who have already previously opened the widget will still be able to open it and complete an order.
The manager will still be able to work with reservations. Only the widget on the website and in social networks will stop working.