Your collection Plan A isn't working. Do you have a viable Plan B? That plan could be to convert that account receivable into a note receivable. There is perhaps a subtle nuance in syntax but there is a significant difference in the actual framework that could make this a viable payment option. While this may not always be your first choice as an alternative measure, it very well may be a worthwhile go-to option that could provide you with some added assurance that you will be paid.

Tell the client that you are under a lot of pressure to pursue the legal remedies available to you but that you prefer to work something out. The client convinces you that you are going to be paid, but just not right away and they may require at least three months to pay you. Your client seems to have been using you as his bank anyway, so this might be a good time to make it official and ask them to sign a Promissory Note. If your debtor is sincere about their intent to pay, then they will agree to do so. Otherwise, this could be a good indication that they have little or no intent to pay you and you should proceed with whatever it takes through legal means to get paid. 

While there are many templates that you can find online, I would suggest that you have an attorney draft an initial note tailored to your business for future use. At the very minimum, I always include a Personal Guaranty and a Stipulation for Settlement and Confession of Judgment. Your attorney can help you draft templates for both of these. Here are a few things to keep in mind:

1. Negotiate terms and interest and see if a security interest in property is possible
2. Explain documents that you will send
3. Clearly define the events that will constitute an event that will make the note payable on demand (i.e. failure to make an installment payment, filing of bankruptcy proceedings, etc.)
4. Be sure to execute the note with signatures of the right individual as maker of the note (i.e. officer, partner, or managing member)
5. Set up a follow-up for installment payments or when note becomes payable.
6. Be prepared to make good on all your recourses should they default on any aspect of the note.

I have had great success with every note that I have issued. Primarily because, if done right, it creates a higher level of urgency from the client to pay. I feel that they are advantageous because you are able to find out sooner rather than later if your debtor has any intention of paying you and because it is much easier to sue on a Promissory Note than it is to sue for your product or services. Other benefits are:

1.  It cleans up your aging! When a company sells goods or provides services and then bills the buyer of goods or services at a later time, the asset on your books is known as an account receivable. However, when you obtain a signed document containing a written promise to pay a stated sum for a specific date or 'on demand' (a Promissory Note) in its place, the obligation then becomes a note receivable. In essence, the promissory note pays off the receivable. Depending on how much time you give your client to pay the note, it could either be classified as short-term (current) or long-term (non-current) asset on your balance sheet. Generally, if the term is less than a year to pay it would be called a short-term note. By getting it out of your aging, you should be able to have a more specialized focus and collection approach that will differ from the rest of your 'Plan A' collection strategies. Besides - I love to see it fall off my aging when otherwise it would sit there for months as it would be in a long-term payment plan. Be mindful, while it will improve your DSO, it does not improve your cash-flow.
2. The Note can be secured! While your product or service may have been released without an adequate credit assessment, you may have a second chance to get that personal guaranty or security interest.
3. You will now have a document signed by the client. That preempts any future claim that payment is being withheld due to deficiencies or dissatisfaction with your product or services.
4. You should be able to get a better return on your money than if it were sitting in the bank. With the current costs of lines of credit being so low, it may make good sense to become your client's bank.
5. It also gives the customer a 'do-over' which may help them get back into your good graces. Often times our clients just need to make more manageable payments over time to get caught up. This may prove to be of great assistance to your client who may not have the means or discipline to do so on their own.

While it may take some practice to recognize when to use this means or to convince your client to sign a Promissory Note, you should have the confidence knowing that you have just as much right to ask them to sign the note as they did in asking you to 'carry' them for the time leading up to this.