The email doesn’t look right when pasted

The button or formatting disappeared

• Make sure the new message is in HTML, not plain text. In Outlook: Format Text › HTML. In Gmail, turn off Plain text mode under the three dots.
• Paste with an ordinary paste (Ctrl+V, or Cmd+V on a Mac), not Paste as text or Keep text only.
• Press Copy email again just before pasting: copying anything else in between replaces it.

The font is different from the rest of my email

Open the template under Templates and set Font and Size to Outlook compose font and Outlook size. The message then takes on whatever your own compose font is. See Templates: your emails and texts.

The button has square corners

That is Outlook for Windows: it draws buttons with square corners. Your customer may see round ones, depending on their mail program.

I’d rather not have a button

Under Settings › Appearance, set Link style to Text link. See Your chalk colour and how the link looks.