Rising action is the long middle where stakes escalate, obstacles compound, and the protagonist is pushed toward a breaking point. Each complication should raise the cost of failure or narrow the character's options, building pressure toward the climax.
Sagging rising action is the most common structural problem in a draft — scenes happen, but the pressure doesn't increase. The test for each scene: does it leave the character worse off, more committed, or more exposed than before?
Example
Each attempt to repay the debt fails in a way that deepens it — until the only option left is the one the protagonist swore she'd never take.