Let most of your transactions pass through bank. Have a structure in place where all transactions are documented and make sure a transaction doesn't start and end with one employee
Report Mercy's answer
Is managing money the root of the problem? Normally, this may not be the case for a Startup situation.
For money management at the start: 1. record all money in and out + document all source document 2. strictly have bank accounts or petty cash only for business only 3. Generate cash flow report on a daily, weekly, and monthly basis
As mentioned, usually, a Startup situation's top challenge shouldn't be managing money, make sure you know your business status well.