Hello,
My apologies, you should add quotes around the url since it contains ampersands. And I forgot to add a slash to /dev/null before. So the command should be:
/usr/bin/curl -sk 'https://mydomain.com/?__wallets_action=do_cron&__wallets_apiversion=3&__wallets_cron_nonce=0227e9c5029dxxxxxxxxxxxxx' > /dev/null 2>&1
Without a shell it is going to be hit-and-miss before you figure out the exact command since every system is different, but I think the above will work.
Let me know if it doesn’t.