Undated cheque was given by client but client asks me continually not to deposit it

The receipt is irrelevant. It only means that you acknowledge that you were given a check, not that the check was any good.

Since you have not yet started the work, I recommend that, if you have something more productive to work on, you simply return the check and drop the client. It is clear that this client will be a struggle to work with, even if he eventually comes up with the money for the deposit.

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If you had already done some work on the project and need to get paid:

It is likely that if you deposit the check, it will bounce (Not Sufficient Funds). If you do decide to deposit the check, be prepared for that possibility and do not spend the money right away. If you go directly to your customer’s bank and show them the check, they could probably tell you whether or not the account has enough money in it to cover the check.

If you find out that the money isn’t there, you have a few options:

1. Continue to be patient and give the client more time.

2. Send the client another invoice with a late charge added. Hopefully on your first invoice, you had included a due date and a late payment policy. If not, make sure that you do so from now on. Find out what types of charges/interest rates are legal in your state/country.

3. Threaten to sue or send the debt to a collection agency. Depending on the amount of the debt, following through with this threat might not be worth the expense.

4. Ask for a partial payment. If they don’t have all the money right away, ask for half now, and half later. He might be willing to do this, and then you have a smaller problem to deal with later.

5. Eventually, you may need to simply write-off the debt. Of course, any work that this client wants you to do in the future must be paid in advance.

As you've clarified in comments, the cheque is advanced payment for work you haven't done yet. Given that, unless waiting for this work is actively stopping you doing some other work, I would just drop this and do something else. You can always chase the client occasionally to see if they still want the work or not.

There is no country tag so I will go for France (even though I do not think this is the right country) EDIT: the country tag has been added following my suggestion, I leave the French aspect below anyway in case someone stumbles upon the question.

The cheque

A cheque must have a date on it, it is part of what makes a piece of paper a cheque (it can be written on anything, provided some clearly defined information is there). Of course everyone uses the bank-provided ones, but some elements must still be filled in, including the date. You should have not accepted a cheque without a date on it.

You then have a year and a day to deposit it, some people kindly ask you to deposit it at some specific point in time so that they have funds ready.

Not having funds for a cheque to clear is a serious offence and great problems ahead for the account owner (forbidden from having a bank account (or an extremely limited one)).

The request

When you receive money for a job it is for something. Not necessarily work, it may be used to buy materials. I recently paid ~50% of a job which was not started so that the contractor could order the materials. Then the job was done and the remaining 50% paid.

What the money is for does not matter - you have in your contract "x€ in advance" and you are free to get them. It is a contract so if you do not do your job you may be sued (in France, depending on the exact naming of that advance money, it may be the money or twice the money)

If the money is not in your account then you haven't received an advanced payment, period.

This client is living in your mind rent-free and keeping you from focusing on other clients.

If the work has not been started then then set the check aside and forget about it until this client contacts you. Preferably you would return the check.

I am not sure if this client is trying to dodge taxes at your expense so be wary of that.