You make up the invoices to bill and get paid. Unless your business checking acct. to which the electronic payment is sent is blatantly obvious (say by title or logo) they’ve no way of determining this. Exception being the $20K limit of sales at which they would issue a 1099 to feds.
I’m in that business. Square is fine if you have a micro business selling feather earings at the farmer’s market or something, but if you are doing more than $5,000 a month in sales, you should get a real merchant account. All the better processors have devices like square that will plug into an smart phone or iPad, but the rates should be far, far lower than 2.75%.
Be careful though. There is no reason to sign a long term contract, and you should never be subject to early termination fees. 95% of the processors out there will try to get you to go that way.
I have real expertise on this. If you would like help, send me a private message.