Both Payed and Paid are two words used as the past tense of the word 'pay'. Pay simply means to give money or other compensation to someone in exchange for goods and services. One of the simple facts about this life is that, nothing comes for free, which means you would need to pay for virtually everything you are desiring to get. Pay as a word, can be used as a verb which explains the act of giving something out to someone in exchange for goods and services. It can also be used as a noun, and also as an adjective.
However, the difference between payed and paid is that, paid is the most commonly used past tense of 'pay', even some may not know that 'payed' is also used as the past tense for pay. Payed is also a correct past tense for pay just like 'paid' but it is seldom used. Payed, aside from the fact that it is a past tense of pay, still has other meanings.