# Business rules

Please check the following necessary preconditions to send a message to a buyer:\
\=> This endpoint works only on the Mercado Libre marketplace.\
\=> The only messaging reasons that allow sending a custom text message are:\
·       SEND\_INVOICE\_LINK. Because it is necessary to send the link of the invoice.\
·       OTHER. Free text.\
The other available messaging options create and send an automatic text message template.\
\=> You cannot change automatic text messages templates contents. No, you cannot.\
\=> The custom text message parameter is IGNORED when the messaging reason do not allow custom messages.\
\=> When you send a message to a buyer, you cannot send another message until the receiver acknowledge and reply to the previous message.\
\=> You can attach a document to a message AFTER a you send a first message with no document attached.\
\=> You need to send to the buyer a first message with no attachment and wait for the buyer to acknowledge and reply to this message. Then, later, you can send a new message with a document attached.\
\=> After sending a message with an attachment, subsequent messages to the same buyer must respect the same message reason.\
\=> Maximum size of free text message is 350 characters.