Sale of foreign shares acquired as gift

I was cofounder if a U.S. company. A US citizen incorporated the company in US and later gifted me and my cofounder the stocks of this company. This happened in 2018. Later we raised funding and company has grown reasonably. I quit from the company in 2020, today I am selling a portion of my shares to my cofounder. 
 

I believe i can mention P0001 as the purpose code. For that purpose code bank requires proof of holding, sale agreement, and proof of sending money abroad during purchase. Since these shares are gifted I do t have the last document. Can I just submit the gift deed instead.