Upload a Blob as a regular file

I have a server running Laravel, hosting an endpoint expecting a file parameter, upon which it validates the rules required and image.

In Javascript, I use Axios to send a HTTP request containing a blob of type image/png. Code example:

const data = new FormData();
data.append('file', blob);
axios.post(submitUrl, data).then(r => console.log(r));

I can’t seem to get that request to pass Laravel’s validation, reporting that the file-upload has failed and responding with 422 Unprocessable Entity.

How do I get Axios to send a blob, just as a regular form would upload an image?

Things (all of them at once, and invidually) I tried so far:

• Wrapping the blob in a File object, specifying it’s lastModified parameter and filename;
• Adjusting the Content-Type header to reflect the Blob MIME type;
• Sending it as base64 instead of blob;
• Just using fetch() and making the request body contain the image.

So far all my attempts are unsuccessful. Thanks in advance.