I have created a new invoice template but it will not open. I click on the customise button and choose my newly created template but it doesn't do anything.

Hello Donnycalder@tisc, Welcome to the Community! Thanks for reaching out about the invoice template not opening. When you click on customise and tick the invoice template you wish to use it does not change anything on the page you use to create the customer invoice, however it should change when click on the print preview of the invoice. When you click on the print preview after ticking in customise the one you want to use can you see the difference?