Canonical struct member names cannot be repeated:
{% include “docs/reference/fidl/language/error-catalog/label/_bad.md” %}
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0090.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
Even though myStructMember and MyStructMember look different, they are both represented by the canonical name my_struct_member. You get the canonical name by converting the original name to snake_case.
To fix the error, give each member a name that is unique after canonicalization:
{% include “docs/reference/fidl/language/error-catalog/label/_good.md” %}
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0090.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
See fi-0035 for more details on why FIDL requires declarations to have unique canonical names.