In many cases, we will use verification codes to log in to an account or activate an action. If you don't know what a verification code is, please check this articleto get a basic understanding of it before you move on.
Usually, a verification code is sent by the system through text messages. People sometimes look for services to receive verification codes. Why do they do that? It's usually due to tricky reasons.
For example, an online merchant is doing discount activities, and it only allows each new user to get a discount for one product. You have got a discount, yet you want to get another discount. Certainly, you can't do that with your cellphone number again. So you go to google “verification code online” and there are different websites that provide this service, which is to use a phone number to receive verification code for you, and the service is free.
So now you have a new account, and you can get that discount again and again. This is an immoral practice that we do not recommend.
Another case is that you don't want to expose your privacy to some websites or apps. So you would like to register using a phone number that is not yours but also valid to receive a verification code. To find this service is also to google it.
There are free platforms online that provide this kind of service. The profit model for these platforms is to attract enough web traffic and sell advertisements.