I would say that there is nothing inherently wrong with using a personal CC for business expenses especially if you run your own small business. There are plenty of pass through business entities and sole proprietorships where it's just not necessary to make that distinction. The problem I see here is with the low credit limit, repeatedly maxing out your limit and paying it down several times a month is a red flag in any situation for manufactured spending or even possibly illegal activities like money laundering (not that I'm accusing the OP of any such thing). It's just the common signs that automated fraud-detection and compliance algorithms would be set up to detect.
If you wish to continue using your card for your business you should be asking Sync to raise your limit as high as possible. They are usually known to be a generous lender in terms of granting increases even to thin files and it's usually a soft pull to ask so nothing ventured nothing gained. Remember it's not unheard of for high net worth individuals to have that much spend every month but it is unusual for them to do so on small limit cards. So you just have to convince the bank that you aren't doing anything illegal or against their terms of use and that you really have the cashflow to support that kind of spending.
