Understanding two flags and a dollar sign in a CURL command

The notation being used there $'...' is a special form of quoting a string recognised by a few shells like ksh (where it originated), zsh and bash.

excerpt

Strings that are scanned for ANSI C like escape sequences. The Syntax is $'string'

Example

$ echo $'hola\n'
hola

$

References

• Quotes and escaping
• 3.1.2.4 ANSI-C Quoting