A topic uses Avro with the schema registry in BACKWARD compatibility mode. Which change to the Order schema will the registry accept?

Under BACKWARD mode, the new schema must be able to read old records. "Adding a new field currency with a default value of "EUR"" works. Old records do not have this field, so the reader fills in the default.

The other changes are rejected:
• "Adding a new field currency with no default": the reader has no value to fill in for old records.
• "Renaming total to amount": Avro sees this as removing one field and adding a new required field with no default.
• "Changing customerId from string to int": Avro cannot promote (convert) a string to an int.