If you've been using Hubspot for a little while you may have to migrate the existing account details to what is called a Private App. The previous way of way of working with API keys has been deprecated in favour of Private App which offer a bit more security.
If you have never dealt with API keys before it's not a problem, should just be a case of creating a new Private App and giving it access to the correct data already on your Hubspot account. You give it via the relevant 'scopes', such as crm.objects.contacts, which is likely a scope you have been using if you have been collecting client/customer contact information in the Contacts table.
There is a good short video and more information on this page about how to carry out the migration (it is a short process). This is the view where you choose the scopes the Private App will have access to. This is the
