OStatus: remote interact is broken

https://pleroma.site/ostatus_subscribe?acct=https%3A%2F%2Fmastodon.social%2Fusers%2FGargron%2Fstatuses%2F100662913821329708

the above URL is returning 500, this can be triggered by visit a mastodon page, then click the boost link, it will open this page, input any user@pleroma.site and it will return 500.

and here is the stack trace:

Server: whatever:80 (http)
Request: GET /ostatus_subscribe?acct=https%3A%2F%2Fmastodon.social%2Fusers%2FGargron%2Fstatuses%2F100662913821329708
** (exit) an exception was raised:
    ** (FunctionClauseError) no function clause matching in Phoenix.Template.HTML.encode_to_iodata!/1
        (phoenix) lib/phoenix/template/html.ex:12: Phoenix.Template.HTML.encode_to_iodata!(%{errors: %{detail: "Internal server error"}})
        (phoenix) lib/phoenix/controller.ex:740: Phoenix.Controller.do_render/4
        (phoenix) lib/phoenix/endpoint/render_errors.ex:60: Phoenix.Endpoint.RenderErrors.__catch__/5
        (plug) lib/plug/adapters/cowboy/handler.ex:16: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) /home/pleroma/pleroma/deps/cowboy/src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4