ADDITION_LIMIT error occurs when you have reached the maximum number of Live Credential sets (Item adds) granted to you in Plaid's Development environment. The default Live Credential limit in the Development environment can be either 0 or 5 and requesting Development access can increase this number to 100.
Active Items are counted differently in Development and Production environments. A Live Credential set (Item) in Development is considered "used" and counts toward the addition limit as soon as you obtain a public_token. Each Live Credential set (Item) can only be "used" once and will count toward your addition limit even if you delete the Item or remove the access_token.
You can review the number of Development Live Credentials (Items) used and remaining on the Development overview page in your Plaid Dashboard account. To request additional Live Credentials (Items) in Development, log in to your Plaid Dashboard account and open a case with our Support Team.