Cannot Add Balance, Reached the Maximum Allowed

These errors can appear in the following cases:

• You are buying too much Battle.net Balance in one order, or are trying to add Balance to an account that already has a significant amount on it. Spend some of your Balance before trying to add more.
• The maximum amount of Battle.net Balance you can have on your account might be lower than expected if you don't have an Authenticator linked to your account. To resolve this problem, please add an Authenticator before trying to add more or spend some of the balance currently on the account. 
• You are trying to claim a Collector's Edition on an account that already has the digital expansion. For some games our system will automatically credit you Battle.net balance equivalent to the cost of your original digital purchase. This is to avoid you paying for the same product twice. Spend some of your Balance before trying to claim the Collector's Edition, or add an Authenticator if you do not have one.