Fixed here: improvement: simplify setting valid on `AshPhoenix.Form.add_error/3` · ash-project/ash_phoenix@b136825 · GitHub

What are you calling add_error/3 with? How did you construct the form?

From looking at the source it seems like it matches on the form type (e.g. %Phoenix.HTML.Form{}) and then on the form source (e.g. %Ash.Changeset{}) and delegates to the source’s add_error.

For a changeset, passing a string should be fine:

@doc """
  Adds an error to the changesets errors list, and marks the change as `valid?: false`.

  ## Error Data

  The given `errors` argument can be a string, a keyword list, a struct, or a list of any of the three.

  If `errors` is a keyword list, or a list of keyword lists, the following keys are supported in the keyword list:

  - `field` (atom) - the field that the error is for. This is required, unless `fields` is given.
  - `fields` (list of atoms) - the fields that the error is for. This is required, unless `field` is given.
  - `message` (string) - the error message
  - `value` (any) - (optional) the field value that caused the error
  """
  @spec add_error(t(), error_info() | [error_info()], Keyword.t()) :: t()
  @spec add_error(t(), term | String.t() | list(term | String.t())) :: t()
  def add_error(changeset, errors, path \\ [])