Fingers like lightning
At least it's a good problem to have and in a long term growth sector.
A relative of mine has taken 5 or 6 years to get to this stage with several associates (his services are in PR and marketing, mainly to tech companies.) He has more potential work than he can deliver but is very selective about who he uses. He's picked up a couple of people who used to work in the events industry which has been decimated by Covid.
Fingers like lightning
Nervous Newbie
I used to work direct with a large pharma company. I was working a niche and they needed me. I ran the contract as a business though, with a couple of part time workers helping me as it was 24x7 365 support contract. There was more admin that came with it and getting paid was a pain EVERY time. They had me on 60 day terms on the 5th of the month - so if the 60 days ended on the 6th, then they would pay it on the next upcoming 5th - so up to 3 months for an invoice to be paid. I always had to chase it too. It was very good money, but a pain as well.
My current gig pays me every Friday through an agency, much easier.
Super poster
You are paying the agency 16% to outsource your sales & ongoing customer retention/admin to them. They are also factoring your invoice.
Factoring 90 days is not cheap. Salesmen are not cheap.
I think learning business fundamentals before moving on to client acquisition & ongoing servicing et al is needed here.