The warlock's page has the following feature describing Eldritch Invocations. I have italicized and underline an erroneous sentence that is a copy of a sentence at the end of the feature, also underlined. 

Eldritch Invocations

In your study of occult lore, you have unearthed eldritch invocations, fragments of forbidden knowledge that imbue you with an abiding magical ability. A level prerequisite refers to your level in this class.

At 2nd level, you gain two eldritch invocations of your choice. Your invocation options are detailed at the end of the class description. When you gain certain warlock levels, you gain additional invocations of your choice, as shown in the Invocations Known column of the Warlock table.

Additionally, when you gain a level in this class, you can choose one of the invocations you know and replace it with another invocation that you could learn at that level.

If an eldritch invocation has prerequisites, you must meet them to learn it. You can learn the invocation at the same time that you meet its prerequisites. A level prerequisite refers to your level in this class.