Ability to default the Amount field and make it non-editable for the Car Rental Expense type

Summary:

We wanted to hide the Amount field in the Car Rental Expense type and default its value to 0, so users should not be able to enter any value for this field. We tried hiding the field and marking it as non-required. However, even after setting it as non-required in Page Composer, the system is still prompting us to provide a value for the Amount field.

Can anyone please let me know how this can be achieved?

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):