As you have discovered, you can only add the Record_ID to Airtable's redirect URL.
But there is another problem, too.
The other problem is that Airtable's forms don't redirect immediately. There is about a 5-second delay before the redirect happens, which gives the user plenty of time to inadvertently close their browser window before the redirect even happens.
I can think of at least 2 excellent ways for you to solve this problem:
#1. Recreate your form in Fillout's advanced forms for Airtable. Fillout gives you hundreds upon hundreds of advanced features that aren't available in Airtable's native forms. In your case, Fillout gives you 2 great things: (1) the ability to add an unlimited number of parameters to your redirect URL, and (2) instant redirects with no delays at all. As soon as the user clicks submit, the redirect has already happened.
#2. Instead of trying to redirect the person to Calendly after they submit the form, simply create an automation in Airtable that emails them the customized link that they should click on. So after they hit the submit button, they will receive an email with the customized Calendly link for them to click on.
Hope this helps! If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld