If your customer does not provide you with a DGT-1 tax exemption certificate, this may result in a 20% tax being levied on the goods you import. However, you can talk to your customer and ask them if they have any other supporting documents that can prove that your imported goods are in compliance with the relevant regulations in order to avoid being charged this tax.
Also, you can ask your local Indonesian Customs department for more information about the DGT-1 tax exemption certificate and related tax policies to better understand what regulations you need to comply with.