Hello ​@fumsmgmmsmx, welcome to our community! How crazy that you are getting an error message when you top up your Prepaid credit. Good of you to point this out, let's look for a solution together. Is this a code-based top-up? You can also use this to top up via text message or by calling 1244. Via SMS works as follows: 

• Send a text message to 1244 with the text: BUY <amount> < pin code>.
•  For example, for a top-up of 20 euros with pin code 1234 you send: BUY 20 1234

Will you let me know if it works this way? If not, try it through a laptop to see if it works then. I would like to check with you if everything is set correctly at your Prepaid account. Can you mention your phone number, zip code + house number and your date of birth in your profile and give me a call when you have done this? Then I will check with you right away!