I think you probably need to read this part of the docs about proper error handling: https://www.prisma.io/docs/concepts/components/prisma-client/handling-exceptions-and-errors

Just to quote it, you need to check error with instanceof call to determine what type of error it is, what properties it has, and handle it accordingly.

For example PrismaClientKnownRequestError has code property, but PrismaClientValidationError does not and so on.

Example:

try {
  await client.user.create({ data: { email: 'alreadyexisting@mail.com' } })
} catch (e) {
  if (e instanceof Prisma.PrismaClientKnownRequestError) {
    // The .code property can be accessed in a type-safe manner
    if (e.code === 'P2002') {
      console.log(
        'There is a unique constraint violation, a new user cannot be created with this email'
      )
    }
  }
  throw e
}

Regarding your code, we can't really know what res.json(err); does under the hood, hard to tell why it only returns clientVersion, but just console.log should call .toString() method on the error object and you should get much more info about it, not just clientVersion