Resolved. The discount tier request in the reseller portal's admin area works again.

The fix is live. We are watching whether the discount tiers load normally in the admin area again.

Cause found: the API read the discount tiers address as an account ID and therefore answered "not found". The fix is being checked.

The discount tiers page in the admin area of the reseller portal shows an error. We are looking into it. Based on what we know so far, reseller orders and billing are not affected.