Hi @GinoongBakulaw Welcome to Metamask Community Forum!
There can be number of reasons why your seed is Invalid , either the sequence of words is incorrect or some words maybe spelled wrong or you are placing more than one phrase in the wallet. Please try to write them in the sequence and also try to use dictionary to check the spelling of words that you doubt, as well as check if you are giving space properly. Moreover when you type seed phrase click on the option show the phrase while typing, in this way it will be visible to you and you will identify the problem.