I created an application with Companies House using the “live” environment and generated a key. This should be provided as the username for HTTP Basic Auth, the password is ignored.
Bubble will set empty password as “undefined”. This lead to a wrong encoding for the auth header.
Instead, go in https://www.base64encode.org/ , encode your apikey with : at the end (like 124345dsa5dasda:).
In Bubble, change auth for Private key in header
On right in value, Basic encodedbase64key from encoder