Today in Postal History

This folded letter was sent from San Jose.
The date is established by the dateline on the letter.

The sender, Juan Serigiers - a commission house, had a neat oval stamp to provide a return cachet.

The cover was sent via steamer to Panama where it found a ship bound for New York.

Its arrival in New York was marked by a nice strike of round STEAMSHIP 10 stamp.

The handwriting is very neat and careful.
It is the same as that of the letter on the inside of the sheet.

The letter appears to be interesting.
It's in Spanish but there are some things which make me
think that it might have some further interest, perhaps even historical significance.
For example, it refers to W. H. Seward, Secretary of State, Washington.
It sounds like it might be a bill for a shipment which he directed
or which was guaranteed by the U.S. State Department.

Could someone translate it and see if it is worth displaying in translated form?
Just knowing the content would be helpful.