Receiving service providers may sometimes reject your invoice due to incorrect or missing reference numbers or order numbers. This can happen for a few reasons.
Firstly, if the reference/order number is placed to incorrect field on your invoice, the value is then incorrectly translated and therefore incorrectly placed in your recipients invoice. In these cases the reference/order number can be considered as missing. If you place the reference/order number in the same field as you usually do for other recipients, the problem could be customer specific. That is to say this recipient prefers the value in another place, and you should then inquire this from your customer.
Another reasons why you might get an error message about incorrect reference number, is simply invalid data. Some service providers might have stricter policies when it comes to payment reference numbers and how they are to be formed, for example banks can reject an invoice if contains a reference number with letters on it.
With these errors, it's best to contact your customer and inquire the specifics why they have rejected the reference or order number.