The fake Royal Mail text message below, which appears to be from RMUKSMS, claiming the recipient's parcel cannot be delivered due to an unpaid shipping fee, is a scam. The RMUKSMS scam text is being sent by scammers in an attempt to trick potential victims into clicking the link in it. The link goes to a fake and phishing Royal Mail website that steals personal and financial information.
The RMUKSMS Scam Text

Click the link in the RMUKSMS scam text goes to the fake and phishing RMUKSMS website
The Fake Royal Mail Website

If the requested financial information is submitted on the phishing website, it will be sent to scammers who will use it fraudulently. Therefore, if you were tricked by the RMUKSMS scam text into disclosing your credit card information, please contact your bank for help.