Problem:

The order number is invalid. Invoicing via credit note processing.

Solution:

The order number is mandatory information. Without this information, your documents can not be processed.
Please always use a unique anchor word, for example, ""order number"".
Normally, the unique statement (the anchor word) should have been agreed during the test phase.
Please note that this anchor word, is ALWAYS to be maintained. That is the reason why typing errors within the anchor word also lead to rejections.