We do first decide to use promotion offer, but that only for existing subscriber. But our offer need to provide for new subscriber too. So need to use offer code.

I have the same issue and I submitted a TSI too, however the process not yet start as I used a phantom email as my Apple ID (created long long time ago so that I can use a phantom email as my Apple ID, however, Apple changed its TSI process now and won't use my alternative email), so I need Apple support to help me change the TSI email to my real one in order to start the communication. I guess if support said the issue not happen at his side, then it may be good sign as there may be some settings on the device to make it works.