Did you see this thread? Companies House is (variably) specific about trailing “/”
https://forum.aws.chdev.org/t/api-update-release-date-question-for-trailing-bug-fix/8472
For a “ping” see the following thread. I’m not sure the original “official” source (presumably someone on this or the XML forum?). I would guess - but do not know - this may not affect the rate-limiting allowance either. If concerned you should check that experimentally!
https://forum.aws.chdev.org/t/ping-companies-house-service/1573/7