Iso vs payment processor difference: which should I use? | Payment Gods Forum

Yo, NoncashNate here. So I'm wondering about the whole ISO vs payment processor thing, like what's even the difference and which one should I pick for my small online custom t-shirt shop? I've been selling for about a year now and honestly, I'm lost trying to figure out which route is better for my credit card processing, especially since I'm hoping to scale up soon.