think that's what it is
good luck

Bond markets are markets where bonds are negotiated. In Spanish, these are referred to in different ways. the most common are:

Mercados de renta fija
Mercados de deuda
Mercados de bonos
Mercados de obligaciones

I would choose for the first option, which is the most general and descriptive.

This term is quite straightforward in the finance world and appears in all finance dictionaries.

I attach a couple of links where the term appears.

Un saludo