If the party is asking for a design format, you need to follow the below steps:
Step 1: Go to Administration, then select Configuration, then select Invoice/Document Printing, then select Advanced.
Step 2: then select the sale invoice, then add the format in the sales invoice and configure it by loading the default format, and you can change the setting according to your requirements.
Step 3: For further information, you can follow the invoice design link: https://www.youtube.com/watch?v=GABedZfWZOg.