Blockspring does not charge you for using any connector. Some connectors use other companies APIs. Some of these companies offer their API for free while others require payment.
The following details are also explained on our pricing page:
Many connectors use other company's APIs, such as Twitter or LinkedIn. If a company's API requires you to pay for use, you will need to create an account with that company. You can typically sign up for an account on the company's website. You will then be able to connect your Blockspring account to use the API.