the reason why I bring this up is that you have hit a rate limit and the number of domains you want to work with (circa 100) you should think about getting it once and right
There are multiple validation methods available. (HTTP, DNS) and I think DNS is the easiest for you to setup. It also (in my opinion) is the most flexible to change as while you have a compatible DNS provider
Let’s say in 2 months time you need to add another shop. You will need to add 80+ new records to your DNS again as the challenge codes will not be valid. Doing this by hand is error prone and can lead to you reaching your limit again (for example if you mis-type a record)
Andrei