ORA 00936 error calling a PL/SQL stored procedure from a C# web service

PROCEDURE PROC_NEXT_SEQUENCE(
p_owner varchar2,
p_table varchar2,
p_seq_name varchar2,
p_seq_value out number)
AS
v_sql varchar2(4000) ; v_seq_value number :=0;
BEGIN 
if length(p_seq_name) >0 then v_sql := 'select '||p_owner||'.'||p_seq_name||'.nextval AS NV from dual';
else v_sql := 'select '||p_owner||'.'||p_table||'_seq.nextval AS NV from dual';
end if;
execute immediate v_sql into v_seq_value; p_seq_value := v_seq_value;
exception when others then raise_application_error(-20001, 'Get Next Sequence Failed.. '||sqlcode||' '||sqlerrm);
end;

using System;
using System.Net;
using System.Data;
using System.Net.Http;
using System.Web.Http;
using System.Linq;
using System.Web.Http.Description;
using System.Collections.Generic;
using Oracle.ManagedDataAccess.Client;
using FooBarApi.Models;

    // POST: api/Location
    [HttpPost]
    [ResponseType(typeof(LOCATION))]
    [Route("", Name = "AddLocation")]
    public HttpResponseMessage AddLocation([FromBody]LOCATION Location)
    {
        // Access config file and connect to database
        OracleConnection conn = new OracleConnection("User Id=FOO_BAR; Password=foo_bar; Data Source=FOOBARTEST");

        // Setup call to stored procedure 
        OracleCommand cmd = new OracleCommand();
        cmd.Connection = conn;
        cmd.CommandText = "PROC_NEXT_SEQUENCE";
        cmd.CommandType = System.Data.CommandType.StoredProcedure;

        // Assign parameters
        cmd.Parameters.Add("p_owner", OracleDbType.Varchar2);
        cmd.Parameters.Add("p_table", OracleDbType.Varchar2);
        cmd.Parameters.Add("p_seq_name", OracleDbType.Varchar2);
        cmd.Parameters.Add("p_seq_value", OracleDbType.Decimal, 4000).Direction = ParameterDirection.Output;

        // Execute stored procedure
        conn.Open();
        cmd.ExecuteNonQuery();
        conn.Close();

        db.LOCATIONS.Add(Location);
        db.SaveChanges();

        var response = Request.CreateResponse<LOCATION>(HttpStatusCode.Created, Location);

        string uri = Url.Link("GetLocations", new { LOSEQ = Location.LOSEQ });
        response.Headers.Location = new Uri(uri);
        return response;}