"Refer-Events-At"  HCOLON  LAQUOT  ( SIP‑URI /  SIPS‑URI )  RAQUOT  *( SEMI  generic‑param )

; example:
; Refer‑Events‑At: <sips:vPT3izGmo8NTxaPADRZvEAY22BKx@example.com;gr>