My app doesn't work anymore on my main account. I cloned my app and export it on another account and it's working. I think my main account have a cloud server problem.
Can you be more specific?
You are indicating usage of cloudDB, is this the part that is not working? Are you using the MIT provided cloudDB database or your own redis server ? What are your settings in the designer?
Main account / other account ? What do you mean by this? AppInventor logins or cloudDB credentials?
Please show your relevant blocks, designer screens, any error messages.
I'm using MIT provided cloudDB database. My app is a chat message online. There are no errors messages. My blocks work on my second app (second account). When I send a message, it doesn't appear in the chat on my app from my main account.
Two identical app but the one of my main account do not work.
Does it work if you send a message from the one on your main account to the one on your second account?
Are you trying to do this on one computer. It might be better to use two computers, or even better build an apk and install it on two different devices.
It's a screen error of my app from first account.
I cloned it and duplicated it on a second account and the second is working.
Two account, two different Cloud 
Im using different devices. Smartphone and tablet.
Your answer is in your error: you can only append to a list
When i make another app (type messenger), it's not working (with the same account). So i had to use on another account.