When collecting donations, certain fields are present by default to be filled by the donor, without the addition of any forms on the page like the Name, Phone no., and email. However, if specific information is to be collected from donors, then a pre-payment and/or post-payment form must be added. To add a custom field for donors to fill on a Giving page, you will need to add a field to these forms:
Navigate to Tools > Giving on the admin panel.
Select the Giving page to which you want to make changes.
Then scroll down on the Page Settings tab and select Forms.
Add a pre-payment and/or post-payment form and then click on Edit Form. (Instead of adding a pre-existing form, you can also create a new form and add the custom field there.)
Clicking on Edit Form will redirect you to the form you are editing. If you had chosen to Add Form, it will have the same flow but you will have to name this form and mention how you would like to use the form.
When editing or creating a new form, to add a custom field you will need to select Add a Question / Form Field.
This will allow you to create a custom field of your choosing and you can edit some more options by toggling them on/off.
Once you are done making the desired changes, click on Save Changes.
Save Changes to form too.
Once the field is added it will appear as a new field on the Giving page, and donors will be able to see and fill it while donating.