Shared iPad requires that DEP devices be associated with Apple School Manager. It is not supported with Apple Business Manager or DEP at deploy.apple.com. If you are an education customer, see this article for how to migrate from DEP to Apple School Manager and gain compatibility with Shared iPad.
I'm not sure what technical error DEP is throwing to display that error but it appears that non-ASM DEP is rejecting your PreStage Enrollment settings due to that Shared iPad box being checked. If you uncheck Shared iPad, I suspect the error would go away. If you can file a case with support, we can investigate the specific error and make sure we're displaying a more relevant message if that is in fact what's happening.
