From String to java.security.PublicKey object gaves me an illegal character

I have this method:

public static PublicKey getKey(String key){
    try{
        byte[] byteKey = Base64.getDecoder().decode(key.getBytes());
        X509EncodedKeySpec X509publicKey = new X509EncodedKeySpec(byteKey);
        KeyFactory kf = KeyFactory.getInstance("RSA");

        return kf.generatePublic(X509publicKey);
    }
    catch(Exception e){
        e.printStackTrace();
    }

        return null;
    }
}

This should transform a public key (one of n property in this JSON from Salesforce public key endpoint). In my keys should be kid 208, but:

getKey("pTSWJvy04hAU7ev7wmaTvpwHsEbseuPl0AlwoxPHnmoOIMATRT0eTqYpLJxDp4BHRFxDTrcUKHKVHGIAVut_-l6nkEI6ALOVW9C5PP9bXwqeHJ5tiGA6AMpaY1LsJJOd2lgExr0LHUPF2TtO4LOVmlptyGPTRSWhmRpPSc5bjGFsyTFr78WmeixjEts9icAUCiBDdpwVw9qVdjJPsufyimqp8os5htm-DB_qKsnRwABVSQRKLw2y7Mr7NP31R07Mpr108dLS5Et8tKnFoiX0MHf5BbA50NG3DtyT27nSa14T0IvSWYJQhxPWXYtuXkVldpbZZn8E2B1VpcDXXGnSPXoPstE9BU7w1RaF31UeEsE8sWDFdHgJMUYMfWjxVhdJB_NaVUt7v0X9QPffXcFPWKUUeVx0g_ONMz0bB_HltFSODWJeAvcZXk14u4sjpKXNIiK8dJzMe0Qn10m5nIdVtxzXfKHiDNobX1dMENDplhDMVk1eYS9x8dh90qt68Q59vKusm6iMjSaXtzwMfqJBwNck41e9Pie2m_cdSu-RIq1u3FScGkezzqNvIuzcse2y-6ApHkkaFMVsNw3CbD87LtVgNusuom38UVC1rS0LeLYFinU3hnFwvB1UCv1_0Cs8CmrOmdifqd25aZIDf5p8f3kowq3QY1mNtdQc9-HgZ3k");

returns me an error:

java.lang.IllegalArgumentException: Illegal base64 character 5f at java.util.Base64$Decoder.decode0(Base64.java:714) at java.util.Base64$Decoder.decode(Base64.java:526) at testJwt.testJwt.App.getKey(App.java:52) at testJwt.testJwt.App.main(App.java:76)

What can I do? I'm do something wrong?