Custom oauth2 error auth access token unobtainable

My version of HedgeDoc is: 1.9.9

What I expected to happen:

local hedgedoc instance should send a request to my local oauth server, in order to obtain the authorization token/the token to request the actual user data

What actually happened:

but instead it throws internal server error oauth access token could not be obtained or sth like that. It should only send it to port 8080 but on 8080 there is no incomming request. activated debug for 8080 but still no request to be found.

example that i sent to my local hedgedoc and the error occured after
http://localhost:3001/auth/oauth2/callback?state=tnctuHR0jexdP8ev5xCamZDn&code=eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJBdXRoUmVhbG0iLCJpYXQiOjE3MzQ1NDE5NTcsImV4cCI6MTczNDk3Mzk1Nywic3ViIjoiZGVidWciLCJhdWQiOiIxIiwic2NvIjpudWxsLCJ0eXAiOiJ1c2VyIn0.LfeVDzVhYCkLM07-ehKI_OfHblF6DQMhArg4xJtpzWKMhyX4tWoon48vVZ_uCUGXnE2WqopgHLO9DJDooq_W18y8q6a5kNOg5WTanJ4YsGBfm8aGrmgFDLHwtbnwd3YGHLkBcBrvUEB1m3b_NliiAI6BKSPu4Cezu1RO7jl2rTjQpDqAr_OZgojP_KAyqPUlPHdPlnLvZEXP7JPA09pOqRBJpJL_8HF_8X5qy7j_pBEsH_uU3eoBfrKkp9wMeUyoOaYwV0Uc98N1I7Sqx9aBfJcREG-J6XiIdSsthAPlKwRom--LgDsAGrLyiGQ1u3OUa_5glhRuzeK_L9-XK2zibw