I got my first sponsorship when I was only jumping 1m so it all depends on who you reach out to
Here at my country there is no sponsorsheep, the only sponsors we have are the people that pays for the train of their horses, actually, you do have if you are jumping the bigges international show.
I am in the UK 🇬🇧 and here you can get some sponsorship from jumping unaffiliated but most sponsors come from when you are jumping BSJA and around the 1.20 mark and competing in large sponsored events.
Depends on who you want to sponsor you. But I think you at least have to complete on national level.