If you pay with PayPal, you can avoid adding the mandatory tip

If, in the configuration of your platform, you have the tip for your drivers as a Required Field, when your clients select the option to pay with Paypal, if they have not chosen the tip for the driver, a message will appear mentioning that they need to add it; When they select the amount for the driver, the option to pay with Paypal will appear.

Give it a try