Cannot Upload World to Realm

Whenever I attempt to upload a world to my realm, it tells me that there was an error or the upload was failed. Therefore, I cannot play my desired world with my friends on a realm and this saddens me greatly. I fear that my £3.29 has gone to waste, however I do hope there is a solution and that the money I have dedicated to this endeavour will not have been spent in vain. Thank you in advance for any help.