Turns out we were serializing two parameters in the wrong order.
@ -559,8 +559,8 @@ static u8 *fundee_channel(struct state *state,
state->localconf
.max_htlc_value_in_flight_msat,
state->localconf.channel_reserve_satoshis,
minimum_depth,
state->localconf.htlc_minimum_msat,
state->localconf.to_self_delay,
state->localconf.max_accepted_htlcs,
our_funding_pubkey,