Marketplace was added to Sim Settlements 2 with the 3.0.0 release to allow you to trade for Resources and Supplies.
The goal is NOT for resource trading to replace all other means of getting resources, but instead to augment them, and provide a way to quickly cover shortages.
Marketplace will also unlock when a Caravaneer Services plot reaches Level 2, which will give you access to Priority Shipments.
Your Capital City is by default your Main Settlement (where you have first placed a vanilla Recruitment Beacon, or the Settlement you have set in the City Manager Holotape as your Main Settlement).
A Capital City is required for Trade Agreements. During the quest, Mysterious Benefactor, you will be prompted to select your Capital City.
See Settlements & Cities for more information about your Capital City.
Once a Caravan Services plot reaches Level 2, you’ll gain access to Priority Shipments. To access Priority Shipments, speak to the Caravaneer and select PROVISION.
Priority Shipments will bring up a barter interface where you can buy Resources and/or Supplies. Upon purchasing these shipments, they will be deposited into your Settlement's Virtual Storage in your Capital City. If there is no space for your purchase, it will be deposited into your Inventory.
Purchasing these is like purchasing Shipments from vanilla traders. The Caravaneer will have various packages to purchase in quantities of 100, 500 and 1000.
When a Caravan Services plot reaches Level 3, you’ll gain access to Trade Agreements. This allows you to set up daily purchases and selling Resources and Supplies from Virtual Storage.
Select Provision, Trade Agreements to bring up the barter windows to set up daily purchases and/or sale of various Resources and Supplies.
Trade Agreements can be set up to:
Any surplus that cannot be stored at the Main Settlement will be distributed to the Caravan Network.
By default, Sales are made at 75% of base resource value, and Purchases cost 125% of base resource value.
For example, Wood has a base value of 1 cap, so selling 100 to the marketplace will go for 75 caps; whereas purchasing 100 will cost 125 caps. This incongruence represents the cost of doing business, and mechanically ensures that there is still value in building up a network of plots to produce resources.