Read the following passage and answer the question based on it: As India aims to become a $3$-trillion-dollar economy this year and a $5$-trillion eco...

Read the following passage and answer the question based on it:
As India aims to become a $3$-trillion-dollar economy this year and a $5$-trillion economy by $2024$, major global powers prioritize developing relations with India. Meanwhile, Russia and India, long-standing allies, are striving to elevate their economic cooperation to match their strengthened political ties. Removing barriers to bilateral trade and investments is a current focus for both nations. A significant challenge in trade between Russia and India is the absence of a seamless independent banking infrastructure connecting the two countries. The current trade turnover is about $10$ billion USD, with expectations to triple to $30$ billion USD by $2025$. Mutual investments could reach $15$ billion USD if financial systems are prepared.
Russia is India's top defense supplier, accounting for over $60 ext{ extbackslash}$ of India's defense purchases, including major deals like the $S$-$400$ missile system worth over $6$ billion USD. Despite India's efforts to diversify and localize defense production, relations with Russia remain a priority amid Western pressure. Russia views Western policies as unfair competition aimed at excluding it from international markets such as defense, energy, and expertise.
Defense deals have exposed vulnerabilities in the banking systems of both countries to third-party actions. When US dollar payments were halted in $2018$, India and Russia urgently sought alternatives, including trading in rupees and roubles, euros, or Singapore dollars. This situation highlighted the importance of payment mechanisms, recalling the Soviet-era practice of trading in national currencies. However, today's interconnected global economy limits such mechanisms for global business actors.

Question: What issue has drawn the attention of banking officials in India and Russia?