Hey again! I've researched a bit and it seems that you might have a corrupted inventory since you gave yourself a corrupted item. Could you ask your friend to delete your inventory? He could try to clear your inventory in game or look up this tutorial: https://www.akliz.net/manage/knowledgebase/48/How-to-Reset-a-Playerandsharp039s-Location-and-Inventory-on-a-Minecraft-Server.html
Hope this fixes the problem, good luck!
Scribea's post in Can't join a friends server was marked as the answer