Cookie not accessible in subdomain in nextjs

[smartbite-tech]

Hi, I am facing problem to set and get cookies across the subdomains. let me explain my scenario. so we have a domain and two subomain like localhost.com:3000 & admin.localhost:3000, api.localhost:3000 ( its on single nextjs server I just rewrite the url).
I am trying to set cookie from admin.localhost:3000 but from api.localhost.com:3000 API endpoint, the response header having set-cookie key but its not set in browser. you can check the screenshot

Here is the response & request header:

No cookie set

once I changed the API endpoint to admin.localhost.com:3000 the cookies is working fine. but this is not my case. I need to call all my request from api.localhost.com:3000

Note: I also tried with sameSite key with none, lax. but its no working. need help on this. Thank you

[Velik0ff]

You need to set the domain option to the sub-domain. This allows cookies to be shared with the domain required.

[smartbite-tech]

You need to set the domain option to the sub-domain. This allows cookies to be shared with the domain required.

@Velik0ff I already tried this.

[Velik0ff]

You need to set the domain option to the sub-domain. This allows cookies to be shared with the domain required.

@Velik0ff I already tried this.

I do not know what is the domain set in the environment variable, however, in order for my-site.example.com to have the same cookies as origin.example.com or example.com, the domain field needs to be set to the registered domain by eTLD+1, which given from the examples (my-site.example.com, origin.example.com) should be example.com (the main domain)

I can see that in your case you have used .localhost.com and you should remove the "." before the domain name

[smartbite-tech]

I tried it by removing the . before localhost.com but no luck. As I said in question that if I am requesting to save cooking at api.localhost.com from admin.localhost.com, meaning my requested subdomain is different from the origin subdomain.
Note: If I am changing my requested subdomain same as origin subdomain (admin.localhost.com) the cookie is working.

[Velik0ff]

I just saw that your requests are made with :3000 whilst you are specifying the domain to contain localhost.com. If working on different ports, this would be considered cross-site cookies, thus sameSite field has to be none.

However, this is a big security issue that you introduce and I would advise on doing it only in isolated development environments.

[sandrinjoy]

localhost.com

Bro what is localhost.com ? do you own this domain?