The issue you are experiencing could also be related to the age and “trustworthiness” of your Instagram business account. If this is a new instagram account or one that has limited engagement in the past, it is possible that Instagram is viewing it as having a lower than average trust rating.
Instagram Commerce Eligibility Requirements - Section 4 mentions this topic. Instagram doesn’t provide a way to measure this that I am aware of, but it could be the issue at play here. The only thing we can suggest from our end is to continue your brand engagement, boost your followers and continue to show that you are a real store that sells real products.