If you are a user on a paid subscription but are receiving a notification to 'Upgrade' your plan, you need to first make sure that you are correctly using your team account.
The reason that you are receiving the 'upgrade' notification when using your 'Personal' account is that you need to instead use the 'Team' account(s) which you have been invited to by the primary account owner. You do not need to upgrade.
The primary account owner purchased the subscription for a certain number of licenses and is technically the only user in the organization with a 'paid' subscription. The owner then invited the other users to their 'Teams' which they have created. In order for the invited users to have access to the paid features of the account, they will need to be using the teams which they have been invited to, not their 'Personal' account.
All users in an organization, except for the primary account owner, are still classified in the system as being on the 'Free' plan. Only when the users log in to the 'Team' accounts (that are owned by the primary account owner) will those users gain access to the paid features of the subscription.
For more information about teams, see Teams explained.