Balance of payments is a comparative relationship between all monetary funds received from abroad and all monetary funds paid abroad in a certain period of time. Equal balance of payments is called balance of payments, otherwise it is unbalanced. Total income is greater than total expenditure, which is called balance of payments surplus, or balance of payments surplus; Total expenditure is greater than total income, which is called balance of payments deficit, or balance of payments deficit. Deficit refers to external liabilities, which are generally paid in foreign exchange or gold.

If you understand the definition, it is easy to explain. Since the foreign exchange income is less than the expenditure, the foreign exchange in the market will certainly be insufficient, and the local currency will flood the market and the supply will exceed the demand.