I believe the SMART cards are just for Hawaii residents. As a visitor from the Mainland, I went with the easiest method:
Signed up for the Smart Travels site, one account for each traveler, login in with my email address. Once logged in, these are the only three icons you need to be concerned about:
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Click the Trips image, and enter your flight info. It's a manual thing, but once it's there, the trip will appear as a clickable link in future login sessions.
Click the Apply for Exemption icon and upload a clear image of your Covid vaccine card, showing you've had at least two shots, the latter one at least two weeks before the travel date.
24 hours before your flight, click the Health Questionnaire icon. It asks a half dozen questions about whether you're sick. Once you submit that, you'll receive an email with a QR code that looks like this:
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When you arrive at the airport, your airline should have some sort of check-in place set up to pre-screen passengers. They'll ask you to call up the Trips icon from the above website, which will show the above QR code. (Or you can print it out - easier just to click the Trips icon from the travel.hawaii.gov website.) When they scan the QR code, they'll also look at the comparison of the uploaded Covid vaccine card, and the real card that you brought with you to the airport. Once they confirm it's the same card, they approve your screening. They'll put a wristband on you, and soon after, your Screened status changes from No to Yes. You're good to go.
On arrival in Hawaii, security at the airport will want to direct those without wristbands to a manual screening location. Those with wristbands head to Baggage Claim and out the door. You can remove the wristband anytime after that. You may need to show your QR Code and Screened Status to the rental car or hotel people. Just click the Trips icon again, and it'll be there for them to review. To get into restaurants, you'll need to show ID and your Covid vaccine card. I just took a full-size photo of my vaccine card and driver's license together, and presented that. Nobody questioned it. I left my Covid vaccine card in the room safe, where it wouldn't get lost.
That was my experience, and it was simple and efficient. Hope yours is as easy. (On the way back to the Mainland, nobody asked for anything.)