I can't reconnect existing C5 site to my Project Page in New Community

My existing site (Core Version can’t connect to my Project Page in New Community. Everything looks fine e.g. my site ID is correct, my Secret Key is correct. The site URL is showing registered… but I still can’t re-connect (I haven’t done edits in a year… it used to work just fine.)

I tried re-copying the site ID and Key… didn’t make any difference.

Are there specific SQL DB “configuration” mods I can do to reconnect?

What is allow_url_fopen set as in your php.ini ?