That would be new information for me. My understanding is the USA as well as most other countries can require proof you have the ability to pay all your costs while in each country.
Whether an electronic waiver or requiring a formal US visa, the requirements are here. Regarding medical treatment in the US, if that is your purpose for the trip you need proof that your transportation, medical, and living expenses in the United States will be paid. This may be in the form of bank or other statements of income/savings or certified copies of income tax returns (either yours or the person or organization paying for your treatment).
‘Nothing USA’ requires pre-payment. If you have evidence to the contrary I would be appreciative to know about it.
