In this article, I will explain what CORS and CORS errors are and why you might run into them. I will present possible solutions and explain what preflight requests, CORS headers are, and why they are important in the communication between parties. The article assumes you have some basic knowledge of web development and the HTTP protocol. I tried to write the article in a way that is easy to understand for beginners and fill it with knowledge and try to avoid too many technical nuances that are not tightly connected with the CORS topic. If you spotted any mistakes or have any suggestions, do not hesitate to contact me. In some places, I made a simplification where a service means server and vice versa.