From: Rabbi Moshe Sofer
To: Rabbi Yisrael
The Chasam Sofer rules that the carte blanche promissory note signed by both Shimon and his wife is fundamentally valid and collectible under the Shach, Tumim, and dina d'malchusa. However, since the creditor accepted the orphans' inheritance money as an iska for nearly a full year — agreeing to pay profits rather than applying it against his debt — his conduct demonstrates that he considered the document defective, paid, or forgiven, and unless he can provide a reasonable explanation for this behavior, he has forfeited his right to collect.
Source: Shu"t Chasam Sofer CM §53