After I finally got my large backpack back from the Correos bag transfer service, and was refunded by them. I’m changing over to Jacotrans.

Jacotrans doesn’t require credit card payment, or setting up an advance itinerary or getting on the phone or website the night before to arrange pickup. Just put the appropriate number of euros - typically six or nine, depending on distance - in an envelope attached to your bag. (The hotels generally have the envelopes.) Write the destination city and hotel on the envelope and leave the bag with the front desk before 8:00 am. You don’t need a booking number, since you pay for the bag transfer in cash each day.

(But of course, you do need to have euros in small denominations each day.)

A few photos of the Jacotrans tag:

Bags with luggage tag

Luggage tag