Optional pick-up point selector is an expanded feature of Shipmondo's shipping module for Shopify, and requires your webshop to have access to the Shopify CarrierService API.
There are different ways for obtaining Shopify CarrierService API:
a) If you have the Advanced Shopify plan or higher, then this resource is already included in your Shopify plan and you don't have to do anything.
b) If you have a Basic or Standard Shopify plan that are paid annually, you can get access to the carrier service for free.
c) If you have a Basic or Standard Shopify plans with a monthly subscription, then you can get access to the carrier service for $ 20 a month.
For b) and c), contact Shopify customer service, and they'll help activating the carrier service on your Shopify store.
N.B. If the Shopify CarrierService API is activated after you've installed the Shipmondo app, then you should try deleting/uninstalling the app and installing it again.
Follow this link for more info.