@julien-f Thanks for the help
Having a look at what you tried I had found my mistake on the testing being i removed %24 ($) and not %2F (/) when testing in postman
What appears to likley caused my confusion in the first place as well is when logging is set to Info, spring removed the trailing /, so it appeared as not there.
Setting logging to Debug shows the full URL string that it was sending including the trailing /
The other part that compounded the above is INFO throws a warning that URI will not encode certain characters, which i incorrectly followed as the source of the problem.
For the final "How I confused the hell out of myself", the inital URI was actually working, however it was returning a single json object (correctly as well), however Spring silently ignored this expecting an array and just returned an empty array with it. This is fixed by setting the body from a Record to "new ParameterizedTypeReference<>() {}"
Which I did at one point however did not test again with the original working string and by this time the / was either in the wrong place, which would return no objects, or %24 was removed causing a 500 as having 2 /'s isnt accepted.
Apologies for the confusion and the circle dance.