Add-ons will only run in the version they were compiled for.
Was this JSON add-on compiled for version 25?
Or are you trying to use the 25 add-on?
If anyone is interested:
Tibor has also posted the source code for his AddOn on his GitHub site. To use it in 26, you will have to re compile with the 26.3000 C++ API. I have included Tibor's code in my Python extension "data_access" -- available on my web site.
The commands in Tibor's Python scripts have not changed, so they should work equally well with the 26 compile.
I have the same problem with one of my addons.
in vs2022 i recreated the solution. the cmakeList clearly specifies AC26. made sure I'm using v142 toolset
Cleaned the solution , rebuild it, no errors, but ac26 still won't accept it as a valid addon, with the same error message as OP.
Any help would be appreciated.