Messaging him twice with no reply: is it okay?

Start with what the unopened status actually tells you. It tells you he hasn't looked at that thread. It doesn't tell you he saw your message and chose not to answer. Those are very different situations, and most of the anxiety around this comes from treating them as the same thing. If his profile shows he was active yesterday, and the message still hasn't been opened, he's skimming, not ignoring. If he hasn't been active in days, your message is simply sitting at the bottom of a pile he hasn't gotten to yet.

Check the things you can see. Look at his last active time if the app shows it. Look at whether he's been matching and messaging other people. Look at whether your first message was easy to answer or required a thoughtful reply, because low-effort openers often get skipped when someone's in a rush. None of this proves anything, but it lets you size the situation correctly before you decide anything.

A second message works when it gives him a new hook. Refer to something specific in his profile that you didn't mention the first time, or share a small, relevant thing about yourself that he could react to. Keep it light enough that replying costs him almost nothing. A question he can answer in a few words usually works better than a long message he'd have to sit down and write.

Avoid anything that makes the thread about the silence. Don't mention that you sent a previous message. Don't use the second message to test whether he's reading. The thread should feel like a fresh, easy opening, not a follow-up on an unanswered one. If the second message would read as a cold restart to someone who had seen the first one, that's the right tone.

Set your limit before you send anything. Two unopened messages across a few days is a reasonable effort. Sending a third message, especially one that's obviously a nudge, shifts the situation from light interest into chasing, and that tends to make people less likely to reply, not more. Give the thread about a week after your second message. If he opens the app and still doesn't respond, that's a clearer signal than any amount of further messaging.

If nothing happens, let the match sit. You don't need to unmatch or send a closing message unless you want to. If he replies later, respond normally. If he never does, the match will eventually expire or stop mattering, and you'll have lost very little by stopping at two.