first look at the normal, focusing on \ s {1}
here, because it matches a space, so here matches the third one.
(?<=SERVICE_URL":\s{2}").+(?=")
(?<=SERVICE_URL":\s{0,3}").+(?=")
(?<=SERVICE_URL":\s?").+(?=")
:
does not write OK in zero-width assertions, so this is a loophole in sublime regular search for zero-width assertions? Can"t you add a quantitative limit to a zero-width assertion?