There is a known issue with using Safari to upload attachments to OnBase using Unity Forms.
As a workaround, if you are using a Mac computer, you can upload attachments by using another web browser, such as Chrome or Firefox. Please see our article titled Alternate Web Browsers for links to these downloads.
Individuals using an iPhone or iPad will need to use a computer to upload the attachment, as the issue is due to a conflict with iOS, not just Safari.