The specific problem is that American intervocalic /t/ and /d/ is very similar to Spanish /ɾ/. But if they don't get it right it's not perceived as the right ph

The specific problem is that American intervocalic /t/ and /d/ is very similar to Spanish /ɾ/. But if they don't get it right it's not perceived as the right phoneme. The Spanish /t/ is more dental and the undervocalic /d/ is more of a [ð] but they will sound correct in English.