Gittin 65B

גיטא לא הוי ⁠– עד דמטית למתא מחסיא.

However, it is not a valid bill of divorce until you reach Mata Meḥasya.

ורבי אלעזר אוסר מיד. פשיטא, דהא מראה מקום היא לו!

The Mishnah teaches that if the woman said to the agent: Receive my bill of divorce for me in such and such a place, R' Elazar prohibits her from partaking of teruma immediately. The Talmud asks: That is obvious, as she is merely indicating a place for him to receive the bill of divorce and not stipulating that the divorce is contingent upon receipt of the document in that place.

לא צריכא, דאמרה ליה: ״זיל למזרח, דאיתיה במזרח״; וקא אזל למערב. מהו דתימא, במערב ⁠– הא ליתיה; קא משמע לן, דילמא בהדי דקאזיל מיגס גאיס ביה, ויהב ליה גיטא.

The Talmud answers: No, R' Elazar’s ruling is necessary in a case where she said to him: Go to the east, as my husband is in the east, and the agent went to the west. Lest you say that since the husband is certainly not in the west and the agent will not find him there, the bill of divorce will certainly not take effect until later, R' Elazar teaches us that perhaps while he was going west, the agent happened to encounter the husband, and the husband gave the bill of divorce to the agent.

האומר לשלוחו ״ערב לי בתמרים״, ועירב לו בגרוגרות; ״בגרוגרות״, ועירב לו בתמרים; תני חדא: עירובו עירוב, ותניא אידך: אין עירובו עירוב!

The Talmud cites a related halakha. With regard to one who says to his agent: Establish an eiruv of Shabbat boundaries on my behalf with dates, and he established an eiruv on his behalf with dried figs, or if said to his agent: Establish an eiruv on my behalf with dried figs, and he established an eiruv on his behalf with dates, it is taught in one baraita: His eiruv is a valid eiruv. And it is taught in another baraita: His eiruv is not a valid eiruv.