If you removed a friend from WhatsApp, and now you're trying to add them back, but you're receiving the message "you can't add because they left the group recently," it means that WhatsApp has a restriction in place to prevent immediate re-adding after someone has left a group.
WhatsApp imposes this limitation to avoid spamming or repeatedly adding and removing people from groups, which could be intrusive and annoying for users. The specific time frame during which you can't re-add someone varies, but it's typically a short duration, like a few minutes to an hour.
To add your friend back to the WhatsApp group, you'll need to wait until the restriction period has elapsed. After that, you should be able to add them back as usual. Alternatively, you can ask your friend to rejoin the group themselves by sending them the group invitation link or asking them to search for the group and join it manually.
Remember to always consider your friend's preferences and avoid excessive adding/removing behavior, as it can be disruptive and affect the group dynamics. Communication and respect are essential in maintaining healthy and enjoyable group interactions on WhatsApp.