Supported formats
Buttondown accepts PNG, JPG, and GIF images. SVG files are rejected by default because most email clients don't render them reliably — your subscribers would see a broken image instead.
If you upload an SVG, the API will return a 400 with:
Bypassing SVG validation
If you know what you're doing (e.g. your SVGs are only used on the web archive, not in emails), you can bypass this restriction by providing a X-Buttondown-Live-Dangerously header with a value of true: