As a self employed Insurance Adviser, my business category is:
“64999 - Financial intermediation not elsewhere classified”
I’m just an insurance adviser, yet Monzo cannot offer me a bank account.
Its beyond annoying 
They are pretty choosey on the types of business they accept, there’s quite a few they don’t accept so you aren’t the only one who can’t get an account. It’s a common issue, but you’ll have to find somewhere else 
I strongly recommend Mettle.
With afternoon tea perchance? 