Chase has a form, that the doc fills out, including questions about health and whether they recommend against traveling. Theoretically, they could provide this info in a signed letter, on letterhead, but my experience the couple of times I’ve used it is that they insist on the form.

the form theoretically could be given blank for you to fill out name, date, etc, and put up on the website for that, but unless something has changed, they only make it available to you if you call for it (or maybe you can download if you begun a claim on the website first). Likely a tactic to make it harder to file a claim they will approve.