If you do not have an API key for the Manifesto Documents Database, you can create one via your profile page on https://manifesto-project.wzb.eu. If you do not have an account, you can register on the webpage.
mp_setapikey(key.file = NULL, key = NA_character_)file name containing the API key
new API key
The key is read from the file specified in key.file. If this
argument is NULL, the key given in the argument key is used.