Mautic contact to Sendy contact

I got Sendy new contact to Mautic new contact working

but

I cannot get Mautic new contact to Sendy new contact working

I think it because Sendy require API input and I don't see any api input on your Sendy app .. Just the list id # .. Where do I put in Sendy's API at?

Thank you
Bill

I think I got it working by adding the api key in the custom field ...