4. Within one month of receipt of an application pursuant to paragraph 2, the national regulatory authority shall authorise the surcharge unless the application is manifestly unfounded or provides insufficient information. Where the national regulatory authority considers that the application is manifestly unfounded, or considers that insufficient information has been provided, it shall take a final decision within a further period of two months, after having given the roaming provider the opportunity to be heard, authorising, amending or refusing the surcharge.