Possible Clues:

• Letters of gratitude in a text
• Counterpart of 'pls,' in a text
• Expression of gratitude in a text
• Texter's 'Much obliged'
• Quick expression of appreciation
• Texter's appreciation
• Texter's "Much appreciated!"
• 'Much appreciated,' in a text message
• 1971 sci-fi film '___ 1138'