Caravan screen says "Not enough value for trade agreement" ... help

Total value of goods is 1657 gold and yet it says not enough value for an agreement, what am I missing? Also... Is there a way to know how much minimum value is needed to conduct trade anyway? This is the first time I'm sending a caravan to Enstone.. I can click Accept, but I'd rather hear from all of you first before sending some people to Enstone, it's been a season since the last extortion raid and I feel like they'll be back when the caravan is out. I don't wanna have some people out there while their skills are needed here at home defending it (and doing construction)