What is the ruling of Islamic law regarding the failure to officially register a divorce in court due to not possessing the necessary funds for the deferred mahr, after having irrevocably divorced the second wife with three pronouncements and several months have passed?

Divorce takes effect by utterance, and the waiting period ('iddah (definition)) begins from the moment of utterance. There is no connection between the payment of the deferred dowry (mu'akhkhar al-mahr) and the occurrence of divorce. If the husband is in financial hardship, the divorced woman should postpone demanding the deferred dowry until the husband becomes capable, based on the Almighty's saying: "And if there is one in adversity, then [let there be] a delay until a time of ease." (Quran 2:280) Financial hardship is established by the husband's statement along with his oath, which is affirmed by both Shafi'i and Ahmad. If the husband is capable of paying, even in installments, he must adhere to that to the extent of his ability.