Enter PlayStation Plus code is not working?

So I bought Ps Plus today. Then I switched on Ps4 and went to "PlayStation Plus", then "Join PS Plus" to enter the code. However, there's (for minutes) "Please wait" with a loading sign. I have already tried many things (Internet off / on, Internet check, Ps 4 off / on, log out / log in) but it just does not work. What can I do against it?

* EDIT * By changing accounts, it suddenly worked.