Some sounds seem “deceptively similar.” For Koreans, the /z/ and /j/ sound seem similar; to Americans they are very different. Words like “region” and “reason” differ only by those sounds. Vietnamese speakers struggle with /s/ and /sh/ sounds. Practice with “superstitious” or “special” or “superficial” to make the two sounds close together and make sure you can control your articulation. For Chinese speakers, the /dz/ an /zh/ sounds can seem similar with “major” and “measure”… the vowels are different too, but the two medial consonants also have different air flow patterns. They share the same point of articulation, but differ in terms of breath delivery, so it’s a good idea to focus on clearly distinguishing them in context.
A good rule of thumb is that if two sounds seem the same to you, but are different to native American English speakers, then you probably have to hold that sound longer to really appreciate the differences (in sound and in articulation).