SPFX Help with third-party forms integration

Hi there,

We're currently working on a solution to capture data into SharePoint for a customer. One requirement is to capture signatures and I found a third-party provider "Cognito Forms" (http://www.cognitoforms.com) which supports this and also provides integration with Power Automate so we can easily process submissions.

I've managed to get everything working pretty well but I'm having a bit of trouble integrating the forms themselves into SharePoint. I've created a new SPFX project and have create a webpart but I'm having some trouble with the integration. Their are two methods for embedding are:

Seamless

<div id="form1"> <script src="https://www.cognitoforms.com/f/seamless.js" data-key="Muy2UY3MEke97JKU-QCXPA" data-form="38"> </script> </div>

IFrame

<iframe id="form1" src="https://www.cognitoforms.com/f/XahKK9dVBE6JTM2z_XX_RA/9" style="border:0;width:100%;" height="1035"></iframe> <script src="https://www.cognitoforms.com/f/iframe.js"></script>

Ideally I'd like to use seamless but since they are using these "data-key" and "data-form" attributes on the script block I'm not sure if that would be possible in terms of the spfx framework? 

The iframe method almost works but I can't seem to import the "iframe.js" file into the project. I've followed the steps in the MS documentation (https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/basics/add-an-external-library) but I'm not sure how the iframe.d.ts module file should work and my attempts to create it haven't been successful. The usage is:

Cognito("#form1").prefill({"Name": {"First":"John","Last":"Smith"},"Phone":"8034567890","Email":"Email address removed"});

But I'm unsure how you declare the Cognito(element) function as a type and get it to return an interface with prefil. How do you declare a named function like this from an external source?

I appreciate this might be more of a typescript question but I went through their documentation on declaring modules and was none the wiser.

Any help would be much appreciated.

Olly