How to get order form custom field data on thank you page?

How to get order form custom field data on thank you page? OR We need value of custom filed from InfusionSoft form to pass our third party API (skillcheck).

We have account ID field on InfusionSoft order form, we need to pass the account id field value to our third party api after order placed successfully. How we can achieve this?

Has anyone figured this out?