Yup it's the same HFEA as for the whole UK, but in my case it's the add-on to Feds which exports data and sends to them, plus also the backport, whereby they send back the data in some normalized, verified and often enriched shape (possibly from other sources too).
The add-on consisted of perhaps a dozen forms and a few tables, and was mostly handled by Suez for years. Then in mid-2018 we got the specs for the new interface, where we'd have to send json-formatted data, not xml like we did before. The specs did look cleaner and leaner... on the first look. Technically yes, it's the same kind of API that pretty much anyone uses nowadays. It's the details that didn't make sense, fields which were missing, had wrong or ridiculous definitions and generally strongly proving that they didn't know what they were doing, only a half of a how to.
So for this new interface I wrote the transport mechanism (using json or xml via plain http API wrapper or whatever they had) and left it at that. The bet that their side won't be ready until december 2018 was soon off, because they moved it for later; then all bets were off and I actually don't know what came of it.