The free plan has a limit of up to 20 people per user for the number of contacts outside of their organization.

The Contacts List shows the number of contacts within and outside the organization.
See below for how "within your organization" and "outside of your organization" are specifically defined.

 

Contacts within your organization:

These contacts are users who belong to the same organization as you.
If users are added via the admin settings screen and they are using it together as a single organization, these users within the same organization will be added to each other's contacts.

 

Contacts outside of your organization:

These contacts are users who do not belong to the same organization as you.
When you initiate contact with another user who belongs to a different organization, a contact approval request needs to be sent from either one of you, and you will be added to each other's contacts once the approval request has been accepted.

Once you have been added to each other's contacts, you can send direct messages, add members to group chats, etc.

 

Contacts that have not been approved yet and contacts that still have pending approval requests are not counted in your number of contacts.

 

How to check your number of contacts:

PC Version

1. Click [Manage Contacts] on the upper right of the screen to open the [Manage Contacts] screen.

2. Your current number of contacts is the number displayed in parentheses on the [Contact List] tab.

3. The number of contacts within and outside the organization is displayed at the bottom of the [Contacts List] tab.

 

iOS App/Android App Version

1. Tap [Contacts] on the lower part of the screen.
2. The number shown in parentheses to the right of [Contacts] is the current number of contacts within and outside the organization.