Can I set the direct debit mandate request form to have my default body text?

It's nice to see your post here in the Community, helen6.

If you are referring to add the Direct Debit Mandate Request Form as a body of the invoice you send to the customer,  you can only add it as a text.

Here's how:

1. Go to Settings and select Account and Settings.
2. From the left menu, select Sales.
3. In the Messages section, select the edit (pencil) icon.
4. Check the box for Use greeting, then from the drop-down choose your ideal greeting.
5. In the Sales Form drop-down, select the desired Sales Form type. (For example an Invoice).
6. For the Subject and Email message, type in your own custom messages.
7. Click Save. Then, Done.

To learn more about editing your invoice message in QBO, check out this useful link: How to set up or change customer messages.

On the other note, if you're referring to add the form to email your customer. I suggest contacting the GoCardless Support so they can guide you on how to send the form to your clients.

I'm always up to help if you have other QuickBooks questions. Have a wonderful day ahead!