Under what condition could a slave receive freedom in ancient Rome?

The order of freeing slaves existed in ancient Rome. At that time, slaves were considered the property of either private or public persons. Slaves were freed under the following conditions:

When drawing up a will: then, after paying a certain amount, the slave is released by the heir of the slave owner.

Conducting the trial.

Adding a slave to the lists of citizens.

Later, other methods appeared: a public statement by the gentleman about letting go, drawing up a vacation letter, and others.