I have watched several shows and podcasts on this topic. Its clear that they were in India. Roman coinage was used in ancient Vietnam but that may just have been because it was brought their by Indians. There is some evidence they were in China but its not solid and it may just be that the Chinese knew about the Romans but that the two didn’t actually trade delegations.
IMHO, the only gainsaying comes from landlubbers. From the "Roman trade" keyword: