Hi Rosie,
Thanks for contacting us! Not all fonts support the € symbol, and so if it’s appearing as a ? it will be necessary to try adding that symbol using a different font. If you’re keen to keep the font you’re using, you’ll need to leave a space for the € symbol, and then add the € as a second piece of text in a different font, and position it in that space.
Let us know if you have any other questions!