Hello I have recently purchased the new theme…

Hello,
I have recently purchased the new theme Uku, I have installed it on my wordpress but when I activate the theme, i get this error message:

Fatal error: Call to undefined function has_custom_logo() in /homepages/26/d522366862/htdocs/untrekunefille/wp-content/themes/uku/header.php on line 41

Any idea what might cause this? I have a logo at the moment at the top of my website, could it be why? Is there anyway i can keep the logo in UKU theme at the top of the website?

Thank you!
Violaine.