The scenario you are facing is only because, there is actually no "Invoice" line(it has been deleted) and though you have a "Tax" line.
So, when you are trying to "Validate" the invoice, unfortunately it shows the Warning as there does not exist any "Invoice" line.
Firstly, please try to make sure there exists a "Invoice" line with the taxes and then use the "Validate" button.
Hello Damien Forest,
It works perfectly for us.
The scenario you are facing is only because, there is actually no "Invoice" line(it has been deleted) and though you have a "Tax" line.
So, when you are trying to "Validate" the invoice, unfortunately it shows the Warning as there does not exist any "Invoice" line.
Firstly, please try to make sure there exists a "Invoice" line with the taxes and then use the "Validate" button.
Hope this helps.
Thank you.