Does your Salesforce integration support sandbox accounts?

We use a sandbox Salesforce account to test new Salesforce objects before releasing them to our real Salesforce account. FormAssembly, which we used previously for SF integration, has a checkbox to authenticate its connector with sandbox accounts (see attached image). 

When I try to authenticate my sandbox user with JotForm's integration, it just hangs at the authentication form. The same thing happens when I try to authenticate in FormAssembly without the sandbox checkmark, which makes me think that JotForm does not support sandbox accounts.

At the present our integration only works with the main account, it is not compatible with the sales-force sandbox account