The invoice amount will change with the number of billable collaborators on an upgraded workspace. You can view/manage access for all billable (i.e. non read only) collaborators on an upgraded workspace by going to your account page from a laptop or desktop. From there, just click to the upgraded workspace in the left sidebar.
If you don't want to pay for a collaborator on the Plus or Pro plan, you can either change their permission settings to read only, or remove them from all bases in the workspace.
To adjust access for base collaborators, click into each of the bases they belong to.
To adjust access for workspace collaborators, click Add or manage workspace collaborators at the bottom of the list.
Upon removing billable collaborators or changing their permission settings to read-only(Pro or Plus plan), you'll be auto-issued corresponding refunds of Airtable credits, prorated to the collaborators' remaining paid commitments. The credit refunds will go through a month after your most recent invoice.
Please contact our support team if you have further questions.