Narvuk

@Jim M I have loaded a dev enviroment and the issues comes after api activation

to resolve the issue in my dev enviroment

as you notice the extra contains null, IPS doesnt like the null value where it is in the database
{"1":{"activated":1658857139,"ip":"123.123.123.123","last_checked":0,"extra":null}} if extra is blank or has no results it need to be set to nothing for example
{"1":{"activated":1658857139,"ip":"123.123.123.123","last_checked":0,"extra":[]}}  
this resolved the error on my dev but was unsure where in the php the value null gets set when either using the api to activate the usage of the license
 
EDIT: 
You can pass [] in extra when activate via api to save it going null, but if left blank when sending it causes extra: to become null which throws the error in ACP view license key view. of product

Thank you for coming to us with the issue, yes you are correct the issue with the theme language tab key assigning, for anyone who is installing all 3 versions may encounter this error
i have fixed this and will soon update the package with the fix.