Azure AD B2C Error: AADB2C90278 Unable to validate the information provided

Question

I have setup a custom sign-in user flow on Azure AD B2C, I am creating a user with a POST request to

https://graph.microsoft.com/v1.0/users

on my backend with the following body :

    body = {
        "accountEnabled": "true",
        "displayName": user.full_name,
        "mailNickname": user.email.split('@')[0],
        "userPrincipalName": user.email,
        "passwordProfile" : {
            "forceChangePasswordNextSignIn": "true",
            "password": password,
        },
    }

and I have configured a sign-in user flow with the following properties set to true on the portal:
Self-service password reset & Forced password reset

Once I test my user flow by clicking on "Run user flow" on the portal, and I login for the first time, it redirects me to the change password page and once I change my password, on clicking save, it gives me the "Unable to validate the information provided." all the time

I don't have application insights setup and I can't seem to get to the root cause of the error, I'm requesting for assistance hereNote: I'm keeping the password complex while changing it