Checking the logs on the server found the following error:
Slim Application Error:
Type: FastRoute\BadRouteException
Message: Static route "/client/schedules" is shadowed by previously defined variable route "/client/([^/]+)" for method "GET"
And even though you have actually searched it was unclear what might cause this type of exception.
Organization of routes, if relevant:
#Client routes
$app->get('/client[/{id}]', function(Request $request, Response $response, $args){});
$app->post('/client', function(Request $request, Response $response, $args){});
$app->delete('/client', function(Request $request, Response $response, $args){});
#Credit routes
$app->post('/credits/buy', function(Request $request, Response $response, $args){});
#deliveryman routes
$app->post('/deliveryman', function(Request $request, Response $response, $args){});
#Moip routes
$app->get('/teste', function (Request $request, Response $response, $args){});
#Plan routes
$app->get('/plans', function(Request $request, Response $response, $args){});
$app->post('/plans', function(Request $request, Response $response, $args){});
$app->post('/plans/sign', function(Request $request, Response $response, $args){});
#Responses routes
$app->get('/error', function(Request $request, Response $response, $args){});
#Schedule routes
$app->get('/schedule', function (Request $request, Response $response, $args ){});
$app->post('/schedule/deny/{id}', function(Request $request, Response $response, $args){});
$app->post('/schedule/cancel/{id}', function(Request $request,Response $response, $args){ });
$app->post('/schedule/accept/{id}', function(Request $request,Response $response, $args){});
$app->post('/schedule/accept', function(Request $request,Response $response, $args){});
//client
$app->post('/schedule', function (Request $request, Response $response, $args ){});
#Users routes
$app->get('/login/{type}', function (\Slim\Http\Request $request, \Slim\Http\Response $response, $args) {});
$app->get('/logout', function (\Slim\Http\Request $request, \Slim\Http\Response $response, $args) {});