Money is one of the most practically significant things in waking life, so it's unsurprising that it appears regularly in dreams. But in dream psychology, money rarely means just money — it tends to represent something more abstract that money symbolises: value, power, energy, self-worth, security.
The specific scenario tells the story.
Finding money unexpectedly
Discovering money in a dream — a wallet full of cash, coins on the ground, an unexpectedly large sum — is often one of the more pleasant money dream experiences. It tends to correspond to a sense of abundance, opportunity, or unexpected good fortune in waking life. Something positive that has either arrived or feels within reach.
It can also correspond to recognising your own value — discovering a resource in yourself that you hadn't fully registered.
Losing money or having it stolen
Losing money in a dream tends to correspond to feelings of loss, insecurity, or being depleted in some area of your life. Not necessarily financial — though financial anxiety does produce this dream directly — but also the loss of something valuable in a broader sense. Energy, time, opportunity, a relationship that was a source of nourishment.
Money being stolen specifically tends to correspond to feeling taken advantage of or feeling that someone is taking more than they're giving.
Being unable to pay or running out of money
Dreams where you reach the till and can't pay, or run out of money at a critical moment, are anxiety dreams about inadequacy and shortfall. They tend to appear when you feel that you don't have enough — enough resources, energy, capability, or time — to meet what's being asked of you. The inability to pay is a symbol for the inability to meet obligations.