Failed to parse expression "relay" for key "queue.outbound.next-hop"

[alanbbr]

I'm endeavoring to get an outbound relay set up for stalwart 0.6.0, following https://stalw.art/docs/smtp/outbound/routing/. I have copy and pasted the example with the needed modifications to the remote address and auth information:

[queue.outbound]
next-hop = "relay"

[remote."relay"]
address = "relay.dnsexit.com"
port = 25
protocol = "smtp"
concurrency = 10
timeout = "1m"

[remote."relay".tls]
implicit = false
allow-invalid-certs = false

[remote."relay".auth]
username = "..."
secret = "..."

[queue.outbound.tls]
mta-sts = "disable"
dane = "disable"

But after systemctl start stalwart=mail, the status is failed and the log shows:

ERROR utils: Invalid configuration file: Failed to parse expression "relay" for key "queue.outbound.next-hop": Invalid variable: "relay"

"relay" is in quotes, so I don't understand why it's trying to parse it as an expression instead of just using it as a string. I've tried changing "relay" to "dnsexit", changing the port, and commenting out the auth section. Nothing has changed the message, except s/relay/dnsexit/g for that string change. Does anyone see what I'm not getting correct, or have a working example they can share?

[plinss]

Try:

[queue.outbound]
next-hop = "'relay'"

(note single quotes within the double quotes)

[alanbbr]

The documentation has

[queue.outbound]
next-hop = "relay"

It needs to be:

[queue.outbound]
next-hop = "'relay'"

(single quotes inside the double).