Amazon "gates" certain categories and brands to new sellers until more trust is established within your account. grocery, toys, beauty, and premium brands are all gated as beginners.
Anytime you scan something that pulls up as gated, always request approval. You'll either get
a "congratulations!" and you are authorized to sell the item, which is referred to as "auto-ungating" or
you'll be asked to provide an invoice, in which case just exit out of the request.
The general process of "ungating" with an invoice involves sourcing the gated ASIN from a reputable wholesaler and clearly showing the purchase of 10 or more units. Your invoice must include the company's information (their name and address) as well as your information (name and address as listed in Amazon.) It must also be dated within the last 6 months.
Some categories will eventually "auto-ungate", grocery, beauty, and the toy category will auto-ungate eventually. (It is important to note that premium brands in those categories will usually require invoices. For example, Starbucks, Nike, Adidas, Hasbro, Disney, etc. will require authorized documentation to ungate, even if you can sell other things in the category.)
So should you ungate or wait? I think that depends entirely on your business.
If you have more time than money for your business, I would wait as they auto-ungate.
There are plenty of profitable items in other categories that sometimes have less competition than many toys and groceries do. It might just take more time or stores to find the amount of inventory in those categories you need to send in.
If you have more money than time for your business, I would pay to ungate.
Having more categories and brands opened up helps to maximize the time spent sourcing, i.e. you can drive to a store and source the whole store instead of only sourcing the clothing and office supplies, for example.
My two biggest pieces of ungating advice is to
Keep track of the profitable items you have access to that are gated and pay to ungate those first. It's not worth ungating Nike if you do not have access to affordable Nike.
If you do decide to not wait for grocery, beauty, or toys to auto-ungate, maximize your ungating by also purchasing a gated brand within the category. For example, instead of buying a random toy for $5 a unit, I would pay $10 a unit to purchase the Hasbro, Disney, or Lego toy.