The accounting period is closed and no changes are allowed for this transaction - Zuora Error

This error can appear when processing refunds or cancellations which are backdated to a previous accounting period. This is a Zuora Finance-related error. To rectify this, you will need to speak to your Zuora admin to discuss your options.

In the Accounting Rules section, you should find a rule called "Allow Subscription and Amendments to be created in a closed Accounting Period" which needs to be set to Yes.

You can read more about this in Zuora's Knowledge Center.