If i do a request to the serverside API i get the following error: 

{"errors":["invalid api version: expected 1"],"details":"The API endpoint you tried to access is not available on version of the API you requested "}

The request I use is this one:

https://itch.io/api/1/KEY/game/GAME_ID/download_keys

Has the serverside API changed?

Yes, i am experiencing the same thing. Can you please notify us what changed???

Changes like this really need to be communicated to the developers on itch.io. I am building my license management around this api and if it does not work for days, like now, customers would not be able to activate/use my product. Luckily I haven't finished this yet...

Maybe a server issue? When called with authorization token the endpoint https://itch.io/api/1/jwt/me gives me a 404. Same call worked for years.

Can we get an update on this subject?

For me it seem to work again, looks like itch.io had done a server migration or something similar. At least this is what was written in some other forum threads here. I dont know why WE didn't get an answer in this thread so.... :/

Same, everything is working again.

Yup, working again.