Here below a capture of what I get when I open the dev network tool.
The first one giving a 404 looks like the problem. You said above you can reach https://my_website_address.com/api/v1/info in your browser, is that still the case?
Yes it still is the case.
Which URL is the first request from your screenshot? Did you configure an api url in Vikunja?
My screenshot gives the request in the order. It’s well https://my_website_address.com/ which appearing in first.
The first one is the domain my_website_address.com and ends in /info. What’s the full url?