Validation Error on creation of Manual SSH Connection for Replication Task

I searched several times for anything like this, on the forums and in Jira, but did not find anything.

I'm attempting to create my first replication task to a non-FreeNas box - it's a Ubuntu server running ZFS. The error is as follows:

Error: Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/middlewared/main.py", line 130, in call_method
    io_thread=False)
  File "/usr/local/lib/python3.7/site-packages/middlewared/main.py", line 1084, in _call
    return await methodobj(*args)
  File "/usr/local/lib/python3.7/site-packages/middlewared/service.py", line 395, in create
    f'{self._config.namespace}.create', self, self.do_create, [data]
  File "/usr/local/lib/python3.7/site-packages/middlewared/main.py", line 1084, in _call
    return await methodobj(*args)
  File "/usr/local/lib/python3.7/site-packages/middlewared/schema.py", line 961, in nf
    return await f(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/middlewared/plugins/keychain.py", line 276, in do_create
    await self._validate("keychain_credential_create", data)
  File "/usr/local/lib/python3.7/site-packages/middlewared/plugins/keychain.py", line 412, in _validate
    raise verrors
middlewared.service_exception.ValidationErrors: [EINVAL] keychain_credential_create.attributes.remote_host_key: attribute required

I've attached screenshots below.