I can't update Notability app on my iPad
I have been using Notability on my iPad pro. My current version of Notability is 8.2.3 and the newest Notability app for iPad is 8.4.5. I have not been able to update Notability for some reason. When I press "UPDATE" on the app store, it makes a circle and then goes back to the "UPDATE" button as if nothing happened. No error message. I have plenty of storage space on this iPad. All the other apps update fine. I contacted Notability and they told me to contact Apple regarding this matter. Any help would be appreciated. Thank you.
iPad Pro, iOS 12