Consultants often require a portion of the payment in advance when signing a contract. This is known as an advance payment, where they receive a fixed monthly fee in exchange for being available to work a minimum number of hours. It is important to discuss the terms of payment, but not the rate itself. This is something Alan Weiss taught me. I usually don't talk about payment scheduling until I have presented my full proposal.
The simplest and most straightforward way to do this is to demand payment upon acceptance of the proposal. In other words, nothing is official until there is a check in hand (you can't deposit a signature and people can delay even after signing an agreement). The consultant is paid a lump sum after accepting the finished final work; this is typically used for fixed-price contracts. The consultant sends invoices on scheduled dates, such as when a certain percentage of the work is completed or a milestone is reached. Progressive payments are not allowed on contracts with a term of less than three months.
There are many other examples that I can think of. However, consulting firms need to consider cash flow. In addition, they take some risks, so it's quite fair to pay consultants in advance or on time. Things can happen that slow things down. For example, if you do business internationally, the client may have to carry out tedious checks on corruption and money laundering, which may take time to complete more important transactions, but you may be able to free up some money in advance to cover the consulting firm's services offered on the stock exchange.
Other (probably rare) things can cause total train accidents, such as working with a struggling company that could go bankrupt out of the blue. This agreement saves the company money by not having to hire staff and, at the same time, offers flexibility in the use of the consultant's services. Consultants usually require certain terms, such as paying a percentage of their fees when the company signs the contract. A consultant can be employed by a consulting firm or work independently as a freelancer or independent contractor. Insights and techniques related to solo consulting business and philosophy of working on your own account while providing services are also important.