Salesforce integration: integrate JotForm with custom Salesforce domain

I am currently trying to integrate my jotform with Salesforce and I am getting the following error: "Invalid username, password, security token; or user locked out."

I have a custom domain "mydomain.my.salesforce.com" which will need to be pointed to for OAuth instead of the default "login.salesforce.com". Please let me know what needs to be done in order to make this work?

Sorry, but we will need to send this as a feature request to our back end team. We will not be able to provide an ETA at the moment, but once this feature gets implemented, we will let you know via this ticket link.

In the meantime, you may need to use the default login.salesforce.com.