In this brief guide, you will come to know how to fix “Party not ready and Party Leader quit”.
First, you have to click on the settings icon and select return to the main menu.

After that, tap on the Continue button.

Then tap on the Ready button to fix the error.

If that doesn’t work, you will need to open the Origin first.

And then go to My Game Library.

Tap on Apex Legends, open settings, and select the game properties.

Finally, you have to uncheck “enable origin in game for Apex Legends”.