Can't Oauth in Sandbox environment

I have set up an app and have the public API working fine in my dot net API.
My issue is with attempting to authenticate using OAuth.

I have constructed the URL to “request user authorisation code” and once navigated to it displays the login screen.

https://identity-sandbox.company-information.service.gov.uk/oauth2/authorise
?response_type=code
&client_id=d12c34fa-1111-1111-1111-1e234e5e5f43
&redirect_uri=https://localhost:7009/api/connection/process-callback
&scope=https://identity.company-information.service.gov.uk/user/profile.read
&state=11111111-1111-1111-1111-111111111111_f21be018-444f-4b8f-9486-0e5be2cfa46d

When entering my email it responds with
There is a problem
There is no Companies House account that uses this email address

I have a developer account, and filing account, both with the same email.

I understand this is the sandbox environment but cannot find any documentation on how to create a sandbox user account.

When attempting to create an account through this flow in the sandbox environment using the Create sign in detail link, I am presented with the following screen.

After ending the email, the screen suggests it has been created but no confirmation email is received. Spam folder has been checked.

Attempting to log in again using the email that was just used to ‘create’ a sandbox account still results in the “There is no Companies House account that uses this email address”

I have also tried with the ‘GOV.UK One Login’ to no prevail.

Any help/guidance would be greatly appreciated.

What are you trying to do in the Sandbox please? This is only intended to test the filling elements of the API, of which there are very few at present.

SDN

I am trying to test the OAuth flow.
Then test the available filling endpoints.

Can I ask which filing endpoint you intend to develop, as there are only three options there at present, a change of registered office (we also offer this via our xml gateway), a change of registered email address (a new requirement from recently passed legislation) and a number of insolvency form types (obviously very specialised).

SDN

My plan is to lodge company accounts via the ‘transaction’ endpoint.
Is this endpoint operational?

No, as previously advised, there are only three filing options in this API at present. It is our long term aspiration to add more, but this is a long way off due to all the other work we have to do now, and in the medium future. Accounts filing via software needs be done via our xml gateway.
Technical interface specifications for Companies House software - GOV.UK

SDN

@ChrisL did you find a way to create a sandbox account or log in?