How to solve the problem of 'Undefined array key 'sign'' error when calling Alipay EasySDK using PHP?

The stablecoin trading process includes the steps of registering an exchange, completing certification, buying or selling. First, choose a trusted exchange such as Binance, OKX, etc., and then complete KYC identity authentication, and then buy stablecoins through fiat currency recharge or OTC transactions. You can also transfer the stablecoins to the fund account and sell them through P2P transactions and withdraw them to the bank card or Alipay. When operating, you need to pay attention to choosing a regulated platform, confirm transaction security and handling fees.

iPhone does not support creating contact groups directly in the address book application, but similar functions can be achieved through the following methods: 1. Use the "Group" function in the address book application, click "Edit" > "Add Group" to create a custom group; 2. Add each contact to the corresponding group by editing it; 3. If you need to send a group message, you can create a new multi-person conversation in the information application; 4. Use iCloud or Gmail to synchronize tagged groups to facilitate the management of a large number of contacts on the computer. These methods are used in conjunction with efficient management of contact groups.

USDT cash exchange needs to be operated through a trading platform that supports fiat currency withdrawal. 1. Prepare a trading platform account that supports fiat currency withdrawal (such as Binance, Ouyi, Huobi, etc.); 2. Complete KYC real-name authentication; 3. Bind bank cards or Alipay and other payment methods; 4. Log in to the account and ensure that USDT is in the fund account or spot account; 5. Enter the OTC or fiat currency area and choose to sell USDT; 6. Set the sales amount and match the buyer; 7. After confirming the other party’s payment, click “Confirm Coin Delivery” to complete the transaction. Withdrawal methods include OTC fiat currency transactions, bank card withdrawals and third-party payments, among which OTC is more efficient. Notes include making sure to verify that the money is received before releasing, avoiding frequent large withdrawals, and contacting customer service in time when encountering abnormalities. The key to the entire process is to choose

The ways to obtain USDT include: 1. Purchase through centralized exchanges such as Binance, OKX, etc., which is convenient to operate and supports multiple payment methods; 2. OTC modules are included in the platform for over-the-counter transactions, suitable for large-scale and privacy-conscious users; 3. Use stablecoin exchange platforms or wallets (such as TokenPocket) and decentralized exchanges (such as Uniswap) to achieve cross-chain or cross-currency exchanges; 4. Participate in exchange activities or task platforms to obtain airdrop rewards; 5. Obtain USDT incentives through mining, content creation, community interaction, etc.; 6. Collect USDT directly from other people's wallets, and pay attention to chain type matching to avoid asset loss.

USDT can be purchased through fiat currency trading or currency exchange. 1. Choose a formal platform such as Binance and complete real-name authentication; 2. Bind bank cards and other payment methods; 3. Enter the fiat currency trading area to select merchants to place orders and pay; 4. After payment, the platform releases USDT; 5. You can also use BTC/ETH to exchange USDT through currency transactions; 6. Pay attention to choosing TRC20 chain to reduce handling fees and avoid private transactions.

Determining the depreciation value of iPhone requires multiple factors and comparing different platforms. 2. The first choice is Apple's official replacement plan, which has a simple and transparent process, but the final valuation must be based on the actual condition of the equipment. 3. Third-party websites such as Gazelle, Swappa, etc. may provide higher quotations, but you need to pay attention to describing the real situation and avoiding the charging trap. 4. The core factors affecting value include model and storage capacity, equipment status, operator lock status, etc. Small problems may also affect the quotation. 5. If you pursue higher returns, you can choose to sell privately, but you need to weigh the time cost and transaction risks.

To add widgets to the iPhone home screen, you must first enter the "Edit Home" mode. The method is to hold the App icon to shake it, then click the " " sign in the upper left corner of the screen to enter the widget library, select the required widget and size, then click "Add widgets", and then click "Finish Customization" at the end; common problems include installing the corresponding app first, widgets cannot be directly dragged to the negative screen, and can be reoperated when the " sign is not found; in addition, the negative screen can also be managed separately by sliding to the bottom and clicking "Edit" to improve efficiency. It is recommended to use practical components such as weather, calendar, reminder items, batteries and shortcuts to improve efficiency.

Uninstalling an app on your iPhone does not mean completely deletion, and users can make room while retaining data. If you want to uninstall the app and keep the data, you can go to "Settings" → "General" → "iPhone Storage Space" → Select App → Click "Uninstall App"; if you want to completely delete the app and data, you can long press the icon on the home screen → click "Delete App" → confirm the deletion. The difference between the two is that after uninstalling, reinstalling can still restore the original content, while deleting will clear all data and you need to start the next installation. Before operation, you should clarify the requirements to avoid accidentally deleting important information.