You're reading the documentation for an older, but still supported version (1.33.4).
For information on the latest version, please have a look at 1.33.5.

MESSAGE_POPUP

This structure contains a pop-up message that a DRL program running on the robot controller sends with tp_popup(). It consists of the following fields.

BYTE#	Field Name	Data Type	Value	Remarks
0	_szText	char[MAX_STRING_SIZE]		256-byte message string
256	_iLevel	unsigned char	0~2	Message level 0: Message, 1: Warning, 2: Alarm
257	_iBtnType	unsigned char	0~1	Button type 0: Resume & Stop, 1: OK

Total size: 258 bytes

Defined in: DRFS.h

typedef struct _MESSAGE_POPUP
{
    char          _szText[MAX_STRING_SIZE];  /* message string */
    unsigned char _iLevel;                   /* Message: 0, Warning: 1, Alarm: 2 */
    unsigned char _iBtnType;                 /* Resume&Stop: 0, OK: 1 */
} MESSAGE_POPUP, *LPMESSAGE_POPUP;

typedef MESSAGE_POPUP MONITORING_POPUP;