Log in to your Zoho Inventory organization.
Click on the gear icon from the top-right corner. Select Preferences from the drop-down.
Navigate to Sales Orders under Preferences and add a new custom field of type string. The name of the custom field can be something of your choice (but this name has to be updated inside of the custom function code snippet later).
After creating the custom field, navigate to Automation.
Now click on the button adjacent to +New Workflow Rule.
Out of the four options from the drop-down, select Custom Functions.
Now let's add a name to this workflow rule and make sure that there are no spaces between words.
Select Sales Orders against module.
Add a description if you need one.
Now, the workflow type is going to be Event Based.
The condition to set shall be, "when a Sales Order is created".
Now copy and paste this code snippet inside the deluge pane:
salesorderID = salesorder.get("salesorder_id");
Navigate to this line - lab=cf.get("label").toString(); and replace "label" with the name of the custom field.
Navigate to this line - percent= 3/100 * tot; in order to change the percentage applied.
Alternatively, you can also use a checkbox type custom field. However, you will need to modify the code snippet a bit to make it work.
Note: The credit card charges will be updated to the Adjustments field above the grand total. And the label of the Adjustment field will be changed to "Credit card charges".
Hit Save to finish.
Hence forth, whenever you generate a sales order, you can apply credit card charges to it by typing "Yes" inside of the custom field made by you and a % of the total (as given by you) will be applied to the total amount. Hope this helps you with your sales endeavours.