troubles while trying to export a signed package

Hi everyone, as the title says i can't export a signed package. The first time i had to chage the package name (inside of the AndroidManifiest.xml) which was easy to solve (just add the name) then, i had to add the icons of the app, which i did, but it keeps showing me the following "warning":

but i added them in the sketch folder like this:

any idea on which is the problem?