Hi, can you describe your issue in more detail? What you did before catching the error 😊
Meanwhile, here are the steps to equip the weapon:
1. In hero detail panel, click on one of the 3 empty slots below the character's portrait to open equipment panel.
2. In equipment panel, click on one you want to equip for character.
3. The detail panel of equipment will open up on right side, click on "Equip/Replace/Remove" button.
If you followed the instructions above and still can't equip, let me know, it might be a bug 😊