Format of fields Many to one

I have a table Solicitudes with fields id, name.
I have another table Ejemplares with a field id_solicitud, name_solicitud, among others. id_solicitud is a many-to-one field that points to id in Solicitudes.

When I run a MySQL query with an INNER JOIN it doesn’t return anything:
UPDATE ejemplares
INNER JOIN solicitudes ON ejemplares.id_solicitud = solicitudes.id
set ejemplares.name_solicitud = solicitudes.name
where ejemplares.id = XXXX

Even if I tried to copy id_solicitud to another field, it doesn’t copy anything.

I was assuming that the Many-to-one field id_solicitud would contain an integer, but maybe it contains something different?

A relationship field represents the relationship between two tables.The database table does not have a relationship field.To link two tables, use a foreign key.