Action Type – Custom Text – links don't work

I have a form which, after submission, has a custom text message. That custom text message includes a link to another document. I have tried adding that link using both the visual and the text tabs of the editor in the Form Manager. No matter what I do, it automatically adds quotation marks and backslashes to the URL, making the link invalid. It also refuses to save the clicked checkbox for “open in new tab/window”. Any advice?

https://wordpress.org/plugins/form-maker/