The restricted check feature is available on all paid tiers. For those on the FREE tier, you can upgrade to turn on this feature. You can upgrade by going to SETTINGS > ACCOUNT > SUBSCRIPTIONS.
First, when using this feature it is encouraged that you utilize a Seller Central (SC) sub-account for the restricted check. This way you are not simultaneously contacting Seller Central from two different locations (e.g. you are logged into SC on your laptop and also checking restriction status via SP MOBILE). To do this, follow the instructions here. (https://help.scanpower.com/solution/articles/11000036584-how-to-create-a-seller-central-sub-account-for-use-with-the-restricted-brand-item-check-in-mobile-sc)
NOTE: We strongly recommend enabling Two-Step Verification for your Amazon account.