Retrieve Tokens from Interaction_Code

I’m using the sign-in widget in my application.
My okta app is Web.
I’m able to authenticate in Okta and I’m redirected to the configured page with the interaction_code parameter filled in.

I’m then calling{client_id}&client_secret={client_secret}&grant_type=interaction_code&redirect_uri={redirect_url}&code={code}&code_verifier={code_verifier}

as per the information here OpenID Connect & OAuth 2.0 API | Okta Developer

but I keep getting the error 400 Bad Request

“error”: “invalid_grant”,
“error_description”: “The interaction code is invalid or has expired.”

Any ideas?