To add Terms & Conditions on your invoices and quotes, you have to go in Settings > Document and email configuration. You select the configuration in which you want to add your Terms & Conditions and you click on the Terms and footer tab.
You then add your text, format it as you like (with bold, italics, columns, etc.) and you click on Save. These Terms & Conditions will automatically appear on every document you create with LSP.expert.
If you want your Terms to be displayed on a separate page, you can tick the corresponding box in Settings > Document and email configuration > Terms and footer.
If you add your Terms & Conditions in your configuration after having already created documents, you can regenerate them (= click again on Actions > Generate PDF) to add your Terms & Conditions on these documents. Don't forget, in this particular case, to click on Reset in the Terms part (at the bottom of the document) and on Update terms and notes.