POST https://id.twitch.tv/oauth2/token?client_id=nt_secret=nyo51xcdrerl8z9m56w9w6wg&grant_type=client_credentials

This POST request - if attempted with curl in CMD or windows subsystems linux, you need to escape &clientsecret &granttype with preceeding escape\

e.g.

POST https://id.twitch.tv/oauth2/token?client_id=uo6dggojyb8d6soh92zknwmi5ej1q2\&client_secret=nyo51xcdrerl8z9m56w9w6wg\&grant_type=client_credentials

otherwise you WILL get missing client_secret regardless what you try, nothint about the actual curl gives you any hint regarding this.