Form embed not working on Squarespace (personal plan)

I have a donation form that has been successfully embedded and used in other coda docs, and when I insert the html embed code provided by Coda (using inspection tools), it works like that. However, using the “Embed Block” of Squarespace, the form just renders the word “null” and no iframe or any hint of what the null means.

Btw, I tried both the url for sharing and the url generated specifically for embedding (in the src="..." part of the embed code.)

So it is likely an issue with Squarespace, but I did see a hint on their documentation that these kinds of embeds should support oEmbed, otherwise it won’t work.

Do Coda forms not support oEmbed? Or is there some other problem?