ASIN code:
If the link you are getting looks something like this (for some reason)
https://www.amazon.co.jp/-/en/gp/product/B076GYXJNH?ref_=dbs_m_mng_rwt_calw_pa_tkin_5&storeType=ebooks (Ignore the code thingy. The full link wasn't showing otherwise.)
the ASIN code is between product/ and ?ref...