I agree that they should offer private and anonymous payment like monero and cash. They do talk about using a VPN and Tor to hide your IP but its kind of hidden in the footer.
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You can pay for any Proton subscription with Bitcoin — but it won’t appear as a payment option when you first create your account.
To use Bitcoin, create a free Proton Account, then upgrade to a paid subscription in your account settings.
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We accept cash payments in US dollars (USD), euros (EUR), or Swiss francs (CHF).