This is likely one of two issues.
Your candidate doesn't have an email address
If your candidate doesn't have an email address, we don't let you add them to a sequence with email stages.
Either add an email address to the candidate, or create a sequence with only InMail stages.
You didn't save your sequence
To prevent your sequence dropdown from being too cluttered, we don't include sequences that you didn't save. You can see if a sequence wasn't saved if it has a "Draft" Status.
To save your sequence, click on it -> press "Next: Review and Configure" in the bottom right corner:
And then press "Save" in the bottom right corner:
Refresh the page
If neither of these are the case, try refreshing the page. If the issue persists, contact firstname.lastname@example.org or chat with us.