API Access or APEX Rest Services are not related to the Tuvis Permission Sets
API Access needs to be granted to users/profiles in order for Tuvis to be able to communicate with the SF instance.
In order to resolve this issue, please ask your Salesforce System Administrator to enable the affected User via the "Profile" section in the "Setup" settings:
Setup > Profile > Select Profile > Edit
Once you click "Edit" on the profile that needs access you will need to locate the "Administrative permissions" section and check "API Enabled" and “Apex REST Services” options
Once the Salesforce User has had the "API Enabled" and “Apex REST Services” are checked and the configuration saved the above messaging will no longer be displayed.