new wordpress install cannot upload or install plugins through wpmudev dashboard

just installed a new multisite with "one of those" - wordpress installers built into cpanel at SiteGround.

getting the following error (screenshot) when trying to upload through admin and wpmudev dashboard is not allowing either.

i tried to click on the little "?" (screenshot) to get more info but no luck.
tried live chat and ticket support there (SiteGround) but no luck yet.

"Support Access Granted" luckily seems to be working.

any kind assistance please ?

i asked them about file permissions, caching etc. but no definite solutions yet.