Invalid OAuth response from oidc.<provider_name> - firebase-authentication

Question

I am trying to add Azure B2C as on OIDC provider for Firebase Auth. The implicit flow works fine but the code flow fails with either of the following errors :
Malformed response cannot be parsed from oidc.<provider_name> for CODE_EXCHANGE
or
Invalid OAuth response from oidc.<provider_name>
On investigation I found that the last call where this failure happens is this :
curl --location --request POST 'https://www.googleapis.com/identitytoolkit/v3/relyingparty/verifyAssertion?key=<web_key>' \
--header 'Content-Type: text/plain' \
--data-raw '{
"returnSecureToken" : true,
"requestUri" : "https://<firebase_project_name>.firebaseapp.com/__/auth/handler?state=<state_goes_here>&code=<authcode_flow_code>",
"postBody" : "providerId=oidc.<provider_name>",
"sessionId" : "<random_session_id>",
"autoCreate" : true,
"returnIdpCredential" : true
}'
Response for this request comes as :
{
"error": {
"code": 400,
"message": "INVALID_IDP_RESPONSE : Invalid OAuth response from oidc.<provider_name>",
"errors": [
{
"message": "INVALID_IDP_RESPONSE : Invalid OAuth response from oidc.<provider_name>",
"domain": "global",
"reason": "invalid"
}
]
}
}
I tried checking Firebase logs but no helpful information available. However, I did noticed that Firebase exchanged this code for the id_token successfully from Azure B2C before failing and returning 400 error.
Any help in this regard?