In general, if you subscribe to something through Roku you can only use the subscription on a Roku device and it's even worse if you subscribe to anything through The Roku Channel. Try logging in on the Max website using the email address associated with your Roku account (visible under Settings->System->About). You may be able to use the "forgot password" option to get them to send you a password that you can use on any device, but there's no guarantees. Most people here would advise never subscribing to anything through third parties like Roku, Amazon, Apple, etc. to avoid such headaches.
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