HTTP 301 returned from registered-email-address/company/{company_number}/eligibility

I’ve been trying to change a test company’s registered email address but I get a 400, bad request whatever I try.

To troubleshoot I thought it would make sense to first check the eligibility of the test company for a registered email address. However, when I make an eligibility request to:
https://api-sandbox.company-information.service.gov.uk/registered-email-address/company/{company_number}/eligibility
I get HTTP 301, moved permanently and ‘/registered-email-address/company/eligibility’ returned in the location header. That URL makes little sense as it does not take the company number anywhere.

Should I get a meaningful response from:
https://api-sandbox.company-information.service.gov.uk/registered-email-address/company/{company_number}/eligibility
Or do I need to use a different URL?
Or is it simply that the eligibility service is not available in the sandbox?

I have passed your query to our development dept for an answer and will update here.