The number of contacts in a plan refers to the total number of customers you can invoice.
Let’s take an example where a person subscribes for the Basic plan. As per the plan, he can invoice only 50 customers. The customer can’t invoice more than 50 customers as it exceeds the plan limit. The only way to invoice more customers is by upgrading to a higher plan, or by deleting older contacts and their associated transactions.
and GST filing.