I’ve run into something similar before, especially on the Free Tier where invite emails sometimes get delayed or filtered out.
Here are a few things you can try:
Check the user management section to see if the invitation shows as “Pending.” Even if the email doesn’t arrive, the invite might still be active.
Try resending the invitation from the admin panel. Sometimes it can take up to half an hour for the email to process.
Ask the recipient to check spam or junk folders. Gmail and some custom domains occasionally filter Atlassian messages by mistake.
If nothing helps, you can manually add the user again using the same email to trigger a new activation.