Cant upload plugins including WMPDEV to my site

hi there , please can you help me. I am having real issues with plugins on my WP site. I have tried to install your WPMDEV dashboard plugin but it isn't showing in either my WP dashboard or my WPMDEV.

I'm also noticing that in my WP dashboard, despite updating plugins that are showing as needing updates, the updates don't seem to actually 'stay' updated. I've disabled as many plugins as possible but really struggling to see what the problem is here.

I also can't install the latest WP update either.

PLease can you help me with this. I'm trying to add http://www.remarkablepractice.com to my list of managed sites in WPMDEV.

Thanks

Sally