See that `${1:$(string-inflection-upcase-function yas-text)}` is used 4 times.

act.txt

# -*- mode: snippet -*-
# name: action
# key: act
# expand-env: ((yas-indent-line 'fixed))
# Depends on string-inflection package
# --
export const ${1:$(string-inflection-upcase-function yas-text)} = '${1:$(string-inflection-upcase-function yas-text)}'
type ${1:$$(string-inflection-camelcase-function yas-text)}Payload = {
$0
}
export type $1 = $Action<typeof ${1:$(string-inflection-upcase-function yas-text)}, $1Payload>
export const ${1:$(string-inflection-lower-camelcase-function yas-text)} = (payload: $1Payload) => {
  return {
    payload,
    type: ${1:$(string-inflection-upcase-function yas-text)}
  }
}