Usually it works like this. Either you contact or get contacted by the company wanting an Instagram promotion. Depending on the size of the company and budget, they may attach a contract or Instagram ambassador agreement. Companies that are familiar with promotions will often send you an Instagram ambassador promo packages like these:
Do you want increased brand recognition? As a social media platform, Instagram is an effective way to do this. With advertising options now available for all advertisers, integrating Instagram with your brand's marketing approach helps build your brand, grow your business, and reach a wider audience and younger demographic.