Create A Block-Compatible Post Via the API

I want to migrate many posts that were create in another system to WordPress.

I cannot find any documentation on how I can format my POST request to ensure the created post’s content renders correctly in the WordPress editor.

I tried copying the content returned from a very simple post (two text blocks, one image block with caption), but this resulted in a post consisting of one text block with an inline image.

Question: how is one supposed to format the content property of a post create request in order to ensure even the basic “text” and “image” blocks are represented correctly in the editor?