Hmm the W3C spec seems to use lower case: https://wicg.github.io/turtledove/#build-trusted-key-value-scoring-signals-request-body

[AcostaDavid73]

Hmm the W3C spec seems to use lower case: https://wicg.github.io/turtledove/#build-trusted-key-value-scoring-signals-request-body
And Chrome's implementation also seems to use lower case: https://source.chromium.org/chromium/chromium/src/+/main:content/services/auction_worklet/trusted_signals_kvv2_helper.cc;l=53

Originally posted by @JensenPaul in #1381 (comment)