Upload errors 219 and 713

Recently I cannot upload files, type does not matter jpegs, pdfs all the same, to a couple of sites. I get either error 219 or 713. I have tried off pc and tablet both the same. On pc have tried different browsers, removing antivirus even tried using a
different ip address nothing changes. What I find odd is that it occurs on the tablet also so cannot blame the pc. It only happens on 2 sites and was fine until last week when it started happening. I had not changed anything either.
Have contacted both sites and only me getting this problem as far as they are aware.
I am a bit lost as to where to start.

I have had this experience with Chatstep. At first it worked and then it just stopped taking uploads of any kind, returning error 219. This was on firefox. I found no fix so used Edge, which worked for a month or so. Then it, too, returned a 219. Same with Chrome. I have no idea where to start. This happened first on one browser, then advanced to others. Turned off my antivirus and firewall, no luck. I usually can figure things out but this one has me totally stumped