The URL parameter "categoryId" can be used in two ways:

• use the unique ID of the group service category assigned by TIMIFY ("categoryId"). In this case, you don't need the QUERY parameter "external"
• use the "externalId" that you added to this group service category. In this case, you need to add the parameter "external" ( for ex.: /?external=1) so the Developer API will search by your "externalId" and not by "categoryId" assigned by TIMIFY

You can add "externalId" to the group service with the Developer API endpoints POST /group-services/caetgories and PATCH /group-service/categories/:categoryId