def METHOD_NAME(cls, project):
    """Method called to retrieve the url used to check for new version
    of the project provided, project that relies on the backend of this plugin.
    :arg Project project: project (:obj:`anitya.db.models.Project`):
    Project object whose backend corresponds to the current plugin.
    :Returns: str: url used for version checking
    """
    namespace = repo = url = ""
    if project.version_url:
        version_url = project.version_url.replace("+", r"\+")
        url = (
            version_url
            if version_url.startswith(cls.prefix)
            else f"{cls.prefix}{version_url}/git{cls.suffix}"
        )
    else:
        namespace, repo = cls.get_namespace_repo(project)
        url = f"https://sourceforge.net/p/{namespace}/{repo}/ref/master/tags/"
    return url