We are aware of an issue that is causing the invoice button to not be available to use on individual orders.
Our engineers are working to resolve the issue.
In the meantime you can still use the batch invoice function.
For instructions about how to do this please head to https://help.brightpearl.com/hc/en-us/articles/212648163-Invoices-and-invoicing-sales
and look for the section titled 'How to invoice sales in batches'.
Thanks for your patience whilst we work to get the issue resolved.
We'll post updates here as we get them