v3 API how to upload images - not attachments

v3 API how to upload images - not attachments

I am using SD+ and the v3 api. I am importing html email as new requests using the api and can add attachments with no trouble. I see that the v3 api for creating a new request strips the src= for <img> tags that contain an inline image. I also see that the built in mail importer will also strip the src= but replace the src with the uploaded version of the inline image to recreate the original email. So, the src will reference a link like .../api/v3/requests/16846/images/14431. That is not an attachment, but appears to be just an uploaded image related to the request number. I can also upload the inline image and then replace the src= to reference the image just like what the built in mail importer is doing. BUT, I have poured through all of the v3 api documentation and searched online to look for an endpoint to upload an image related to a request, but nothing exists.
Can anyone help me upload an image, NOT an attachment for a request?
thanks.

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