Wish your business goes well.

some kind of official end of the letter

顺祝商祺=best regards

在信件结束的时候，顺便表达对你经商顺利的祝福 at the end of the letter,express good wishes to someone in business by the way

That's a good wish normally used in the end of letter. "顺祝“ means " by the way, to wish you", "商祺” means "good business", In whole sentence that means "wish you have a good business".