Hi @Ruben_Olthuis,
Welcome to Airtable Community ! :slightly_smiling_face:
Airtable bills you for the number of users in a Workspace, so if there is more than Collaborator in a Workspace (more than 1 email, lets say) you will be billed for 2 users. If you use 1 email then you will be billed for 1 user (20 USD/month if billed annually and 24 USD/month if billed monthly).
Not sure if that helps.
BR,
Mo