Consult the stock purchase agreement to determine when and how a purchaser must pay for their shares.
In general, the best practice is:
In some cases, a stock purchase agreement may allow the purchaser and company to agree to a purchase date for the shares that is different from the date of the stock purchase agreement. For example:
The purchase and sale of the Shares under this Agreement will occur simultaneously with the execution and delivery of this Agreement by the parties or on such other date as the Company and Purchaser shall agree (the "Purchase Date").
The company and purchaser must keep a record of the purchase date if it is different from the date of the stock purchase agreement. If the purchaser is making an 83(b) Election, the purchaser should be sure it reflects the correct purchase date.
The consequences of failing to follow a proper payment process can introduce a variety of potential complexities. Consult an attorney if you have questions about these potential complexities, as they are very fact-specific.