Similar to issue 40, https://api.cpicpgx.org/v1/rpc/recommendation_lookup?diplotypelookup={"TPMT": {"*16": 1, "*1": 1}}&drugname=in.(azathioprine,mercaptopurine,thioguanine)&order=drugname yields an empty Json response '[]'. So was with the key for *1/*1.
According to https://cpicpgx.org/guidelines/guideline-for-thiopurines-and-tpmt/, TPMT does have a TPMT diplotype-phenotype table. Both *1/*1 and *1/*16 have diplotype and phenotype mapping defined in the spreadsheet.