Some Squad Building Challenges (SBCs) can feel like puzzles designed to drain your coins. These 'boss' SBCs often have very restrictive requirements, such as specific leagues, nations, or high chemistry/rating thresholds. The strategy here is meticulous planning and resource management.
Before attempting, check the market prices of required players. Sometimes, it's cheaper to buy specific players than to use untradeables. Look for 'loyalty' players (those who have played 10 matches for your club) to boost chemistry. Use online SBC solutions as a guide, but always try to find cheaper alternatives using players in your club. Don't rush into expensive solutions.