Since Friday I have been getting 403 responses. I am not sure why as it has worked perfectly for me till now.
It would likely help Companies House if you added which API / end point you were trying to access e.g. main REST API, documents API or the streaming API. It might be useful if you note if you got any other error data (e.g. in the message body etc.) and maybe where you were making the request from (e.g. localhost, via proxy) and how (using Ajax, via a tool like Postman etc.).
If you changed nothing and this stopped working might be worth checking if your IP was blocked (this may happen if e.g. you exceed the rate-limiting):
If nothing else has changed it’s most likely that. Other changes that could cause this would be moving between different servers / IPs or changing implementation e.g. I think you can get this if you’ve called via Ajax but not set up the request in the appropriate way.
It’s also maybe worth checking your account and what - if anything - is in restricted API addresses as that has caused people issues in the past:
In case this was via Ajax, an example of how to debug / fix this: