To Create an Invoice for a ticket with an Fixed contract, follow these steps:

Step 1: Head to the "Billing" section in the side navigation bar and choose "Invoice" from the list.

Step 2: Once you have accessed the invoice section, you will see an option labeled "Invoice +". Click on this button to create new invoice.

Step 3: There will be dropdown menus to select the customer, contract and Template for choosing the relevant option. Upon selecting a customer from the dropdown menu, the corresponding fixed contract for that customer will be displayed. Additionally, users have the option to select a template from the dropdown menu, and they can also add new templates directly from the dropdown.

Step 4: To add a new item into the categories of 'Ad-Hoc,' 'Product & Expense,' and 'Service,' there exist corresponding options labeled 'Ad-Hoc+,' 'Product & Expense+,' and 'Service+,' respectively.

Step 5: Users can manually adjust the input values for 'Tax' and 'Discount', but by default, these values will be determined from the Billing template.

Step 6: To initiate the invoice generation process, users can click the 'Generate & Send' button. Additionally, they can access a dropdown menu located at the top right, labeled 'Generate & Send', providing options to either 'Generate & Save' or 'Save as Draft'.

(Note: Selecting the "Generate & Save" option will open a new window where you can download the invoice using the download button.)