Where they hide
A karmic debt is invisible in the finished number. A Life Path of 4 reached through a total of 13 is read differently from one reached through 22 or 31, even though all three reduce to 4 — so the debt only appears if you keep the working, which is a good argument for keeping the working.
They can appear in any core number: Life Path, Destiny, Soul Urge, Personality or Birthday. The birthday case is the most legible, because someone born on the 13th, 14th, 16th or 19th carries it plainly.
The four
13 → 4, the debt of work. Effort does not convert into result at the usual rate, and shortcuts fail conspicuously. Settled by method: consistent, finished work over a long period.
14 → 5, the debt of freedom. Frequent unplanned change and a susceptibility to whatever the easy escape of the era is. Settled by self-imposed structure — limits chosen rather than imposed.
16 → 7, the debt of ego. The severe one: sudden collapse of whatever the person had built their self-image on, arriving when it felt most secure. Settled by rebuilding differently, which is the part most people skip.
19 → 1, the debt of independence. Situations that must be handled alone, and a tendency to decline help that was genuinely offered. Settled by accepting it.
What this is not
It is not a prediction of misfortune, and nobody should be selling you a remedy for it. The tradition frames a karmic debt as a pattern to notice and a disposition to work against — the 19 who learns to accept help stops running the pattern, and the mechanism is entirely ordinary.
If a practitioner describes your karmic debt as something that can be cleared by a payment, a stone or a ritual, they have left the tradition they are citing.