For completely custom endpoint, you first need to create route. (see Routes - Strapi Developer Docs) and then point it to a your controller.
In you case, you could have something like src/api/<some name of your choice>/routes/<some name of your choise for the router>.js
With something along the lines of
module.exports = {
routes: [
{
method: 'POST',
path: '/requests',
handler: '<name of your controller>.<your action name>',
},
]
}
And then adding a corresponding controller. See Backend customization - Controllers - Strapi Developer Docs.
Hope this helps.