LinkedIn PKCE oAuth2 flow results in Internal Server Error

Question

I am in a process of implementing social login and signup in a React and Springboot application. Google and Facebook works ok, but having the following issue with LinkedIn so far:

When the user is sent to a popup window to perform the authentication, it fails showing an "Internal Server Error" with no further details.

auth flow init error screen

What I did:

1. created an app on LinkedIn, specified the redirect url and used the given credentials
2. created state value, code challenge and code verifier values in accordance with the oAuth2 pkce specifications as well as following the implementation guide (I don't think the issue would be here as it works ok with Google and Facebook, so I'm not copying the actual implementation here)
3. Assembling the url to send the user to sign in (sample: https://www.linkedin.com/oauth/native-pkce/authorization?client_id=86b1js5srepcq3&response_type=code&scope=r_liteprofile&redirect_uri=http://localhost:5555/auth/redirect/linkedin&state=GzrryAkOWFPVTwZoendEPjpk0MfdpF&code_challenge=4tFPOZVOEOHZvg19P7v-cDuz1HL0JyxrM5lI2_JIxt4&code_challenge_method=S256)
4. I tested erroneous scenarios where I'd make a typo on purpose to see if I get more descriptive error messages -> yes, if there's something wrong with the parameters themselves, then the error message tells exactly where the issue is.

I don't see any obvious errors in my flow as well as the error doesn't have any details, so right now I am completely blocked with my efforts to make it work.

Any help massively appreciated!

Edit 1: One possible explanation would be this:

Once you have the app created, please reach out to your point of contact at LinkedIn, and we will enable PKCE OAuth 2 flow for your app.

However I don't seem to find any useful information on how to find and how to contact "my point of contact at LinkedIn". This statement is just plain vague so I am hoping somebody out there had the same issue and managed to get it sorted.