Compliance To GDPR While Partnering With An Indian Shipping Company

I am the owner of a UK based e-commerce platform where we sell clothing from Indian designers to our international customers. In order to cater to this service, we will have to partner with an Indian shipper who will take care of the product delivery from our designer to the customer. However, as per UK data protection policy, we are liable to GDPR (General Data Protection Regulation) which states that for a UK based company, to transfer customer details to another company outside UK/EEA, a non-amendable standard data protection clause adopted by the commission (ICO) will have to be signed by both the parties. I tried contacting so many shippers in India and non of them are agreeing to sign the document. I would like to know if there are any ways in which the shipper in India can be safe even after signing the document so that I can convince them. https://ico.org.uk/for-organisations/guide-to-data-protection/guide-to-the-general-data-protection-regulation-gdpr/international-transfers/