Go Embedded Server Plugin

I’m trying to use a custom plugin written in Go using the embedded server approach, i.e.:

func main() {
	_ = server.StartServer(New, Version, Priority)
}

I see the plugin starting in the Kong logs

e[36mkong_1                             |e[0m 2021/11/07 22:06:17 [info] 1098#0: *22 [session-user:1106] 2021/11/07 22:06:17 Listening on socket: /usr/local/kong/session-user.socket, context: ngx.timer

but each time I try to use it as part of registering an endpoint I get an error saying:

schema violation (name: plugin 'session-user' not enabled; add it to the 'plugins' configuration property

I build the plugin using: FROM kong/go-plugin-tool:latest-alpine-latest and then am using Kong 2.6.0.

Any idea what might be wrong with this set-up? It was working but something changed that broke things but am having trouble pinpointing the issue.