Here, the following issues are discussed respectively: 1. If the payment time is not stipulated or not clearly stipulated in the contract, according to Article 16 1 of the Contract Law, if the payment time is not stipulated or not clearly stipulated in the contract, the method stipulated in Article 6 1 of the Contract Law shall be applied first to determine the payment period, that is, the parties shall decide. If negotiation fails, the relevant terms of the contract shall be followed. Then, how to determine the payment time according to the relevant terms of the contract? It is generally believed that "if the subject matter has a time limit for delivery, it is presumed that the time limit is the time limit for delivery of the price." Therefore, if there is a delivery period of the goods in the contract, it can also be inferred as the delivery period of the payment. Second, the delivery and payment of the subject matter shall be performed at the same time in accordance with Article 16 1 of the Contract Law, which stipulates that the buyer shall pay at the same time when receiving the subject matter or obtaining the subject matter documents. In fact, it requires the seller to fulfill the obligation to deliver the subject matter while fulfilling the buyer's payment obligation. At this time, either party can invoke the right of defense to perform the corresponding obligations before the other party fails to perform the payment. However, if the seller waives the right of defense at the same time and delivers the subject matter first, according to Article 16 1 of the Contract Law, the time when the buyer receives the subject matter or takes out the documents of the subject matter is the time when the buyer should pay. Since the seller has delivered the subject matter, if the buyer fails to pay the price, it will constitute a breach of contract, and the seller may require the buyer to pay the price and liquidated damages for overdue payment. Three. If the time of payment is not stipulated or the agreement is unclear in determining the limitation of action, the buyer shall pay the price to the seller at the same time as receiving the goods. According to the above provisions, after the seller provides the goods, if the two parties fail to agree on the time limit for debt performance, the two-year statute of limitations shall apply from the date when the buyer receives the goods. The date of receipt is generally based on the receipt signed by the buyer or the delivery date agreed in the contract. Of course, as a seller, it is very important to stipulate clearly the time, method and liability for breach of contract in the contract, and it also needs special attention. If there is no agreement on the payment time or the agreement is unclear, it will be regarded as a major defect of the contract.