SHA256 checksum at https://services.gradle.org/distributions/ are referenced by a server as:
In prevents browser from having it opened directly in the browser window as a text file and the file has to be downloaded to see its content. It in turn, makes it harder to just open the file to copy-paste the value calling Gradle wrapper task:
./gradlew wrapper --gradle-version xxx --gradle-distribution-sha256-sum yyy
Changing the header value (by marking .sha256 files as text files in your web server) should fix it.