Invoice not of valid status for modification

Invoice not of valid status for modification 

This error means that you are trying to send or resend a payment for an invoice has already been sent and/or paid and so cannot be modified in Xero.  If you send a payment then the Xero status must be Awaiting Payment for it to accept and apply the payment.

To prevent duplicate invoices from getting created in Xero Xeroom uses a flag so that an order can't be reposted once sent.  To resend an order that has already been sent but to create a new duplicate invoice in Xero then use the Resend button or Batch Resend which will use the same invoice no with an A/B/C... suffix to make it clear that they are duplicates in Xero.

In certain situations this may be wrongly set eg if you set a numbering sequence in Xeroom with a start no that conflicts with historical invoice numbers of the same in Xero.  Xero can't create the invoice as an invoice already exists and so will generate this error.  Fix this by using the Xero numbering option in Xeroom or removing the start no or else setting it to be larger than the existing range of numbers in Xero.