To leverage Archera Guaranteed Reserved Instances (GRIs), you need to be able to sign up and use the AWS RI Marketplace. See the following: https://aws.amazon.com/ec2/purchasing-options/reserved-instances/marketplace/
If you do not have this enabled for you AWS organization already you will need to request access to the AWS RI marketplace. For this you will need to be logged in as the Root User to your Master Billing Account. You will also need access to the Bank Account information for a valid U.S. Bank Account as well as a Tax ID for your company. This is a one time setup step per AWS organization
Those who cannot use RI marketplace & hence cannot use GRIs are:
1. Those without a U.S. Bank Account
2. AWS Accounts within an existing re-seller (sometimes ok - please check with us)
3. AWS AISPL accounts
4. AWS China Accounts
5. AWS GovCloud accounts
Additionally, the account that you plan to use GRIs in must be at least 30 days old: https://aws.amazon.com/premiumsupport/knowledge-center/ec2-ri-buy-error/