Monero has three address formats, and some withdrawal forms accept only one of them. If your address is rejected, the format is usually the reason.
The three formats
The primary address starts with 4 (95 characters). Subaddresses start with 8 and let you give each sender an unlinkable address (see subaddress docs). An integrated address is the primary address with a short payment ID, 106 characters long (see integrated address docs).
What to do
- Identify the format by first character and length.
- If a subaddress is rejected, use your wallet's primary address (account index 0); the coins land in the same wallet.
- Use an integrated address or payment ID only if the recipient asks for it.
- Never edit or trim an address by hand.
More on wallet subaddresses: subaddresses in Cake Wallet and Feather.
If a form asks whether to include a payment ID, choose the option without it for a personal wallet. A service that insists on long legacy payment IDs is probably using an outdated deposit scheme, so ask its support before sending a large amount. Also re-copy the address from the wallet: hidden spaces or line breaks from messengers often cause rejections.
Using the primary address instead of a subaddress is safe; you only lose per-sender separation of incoming payments.
Swapping XMR
On the XMR to USDT page you pay to the order's deposit address, so you may send from any subaddress. XMR swaps are floating-rate only; pay within an hour.
FAQ
Why is my Monero address starting with 8 rejected?
It is a subaddress and the service accepts only primary addresses; use the primary 4-address.
Do I need a payment ID for my own wallet?
No; payment IDs were used for shared exchange addresses.