Sir/Madam,
First of all there is no concept of merchant exporter in GST. As an exporter you have procured material at 0.01% in terms of Notification No. 40/2017-CT (Rate) dated 23/10/2017. As this rates are concessional and Notification is a conditional Notification, therefore, you are required to fulfill the conditions mentioned therein. The relevant paras are reproduced below:-
"(iii) the registered recipient shall indicate the Goods and Services Tax Identification Number of the registered supplier and the tax invoice number issued by the registered supplier in respect of the said goods in the shipping bill or bill of export, as the case may be;
(iv) the registered recipient shall be registered with an Export Promotion Council or a Commodity Board recognised by the Department of Commerce;
(v) the registered recipient shall place an order on registered supplier for procuring goods at concessional rate and a copy of the same shall also be provided to the jurisdictional tax officer of the registered supplier;
(vi) the registered recipient shall move the said goods from place of registered supplier –
(a) directly to the Port, Inland Container Deport, Airport or Land Customs Station from where the said goods are to be exported; or
(b) directly to a registered warehouse from where the said goods shall be move to the Port, Inland Container Deport, Airport or Land Customs Station from where the said goods are to be exported;
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ix) when goods have been exported, the registered recipient shall provide copy of shipping bill or bill of export containing details of Goods and Services Tax Identification Number (GSTIN) and tax invoice of the registered supplier along with proof of export general manifest or export report having been filed to the registered supplier as well as jurisdictional tax officer of such supplier”.
From above, it is clear that there is nothing called proof of export to be submitted, but to provide Shipping bill or Bill of Export and EGM to your supplier and also to the jurisdictional Tax officer of your supplier.
Our experts may please correct me if mistaken