Thanks.
OK, did both.
First: Logout and login did change anything (but thanks for the idea).
Second: I added the "=" and thataa... the button "pay with credits" is showing normal and ready to pay.
But then I tried to pay... "There was some errors, please try later or contact the administrator" !
So I tried it many times also with 30min rest between. Did not work.
Then I added 1.- to the User manual as admin (now 6.-) and it works fine.
You can see it at the print-screens.
It was a fresh created brand new user and I give them the 5.- with the osclass_pay option "Add credits to new user".
Is there a rounding error or something like that?
Thanks for your great help.