Unlike the older skins, the Laika skin accepts any interval and amount value provided by a banner and places users on the address page. This makes it open for abuse and more prone to users being affected by issues in banners Currently, URLs like the following examples are possible and will place you on the second page of the donation form (which should only be possible with valid data):

&zahlweise=BEZ&amountGiven=1&periode=24
&zahlweise=BEZ&amountGiven=0.01&periode=6
&zahlweise=BEZ&amountGiven=0.01&periode=8

Since there is no server-side validation for the intervals, it's possible to make a donation with random intervals. This issue, however, has already been documented as part of T222636 and should be fixed separately.

The acceptance criteria for this ticket is that if an invalid amount of interval is entered, users are not placed on the second donation page but are rather shown an error on the first donation page.