Please be aware that this feature is only available on paid tiers. If you are on the FREE tier this feature is not available to you. You can upgrade to a paid tier by logging in at https://unity.scanpower.com and navigating 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). Additionally, if you have people scanning on MOBILE on your behalf or have multiple listing stations, you will want to have a SC sub-account for each user for this same reason. 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: Please make sure Two-Step Verification is turned on for each Amazon account.