Paypal - billing cycle length?

Nothing is more confusing to me than PayPal documentation..

Basically I am trying to set a recurring payment. Each month pay 400.50 Euro for 'Membership' Of course the button they provided failed, but I found some examples and came up with:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_blank">

        <input type="hidden" name="cmd" value="_xclick-subscriptions">
        <input type="hidden" name="business" value="example@example.com">
        <input type="hidden" name="return" value="http://www.example.com">
        <input type="hidden" name="cancel_return" value="http://www.example.com">
        <input type="hidden" name="currency_code" value="EUR">
        <input type="hidden" name="item_name"  value="Membership" />
        <input type="hidden" name="src" value="1"> <!-- recurring=yes -->
        <input type="hidden" name="sra" value="1"> <!-- reattempt=yes -->
        <input type="hidden" name="p3" value="1"> <!-- billing cycle length -->
        <input type="hidden" name="a3"  value="400.50" />
        <input type="hidden" name="t3" value="M">

        <input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_subscribe_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
        <img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
    </form>

What value should"billing cycle length" be - now default 1?
Does this mean once the user clicks my button - a payment will be extracted every month or it will only work one time (that 1 value)?

Solution

According to this PayPal documentation p3 is the subscription duration and should be used in conjunction with the value of t3.

Here's the details from that page:

p3 - Required

Subscription duration. Specify an integer value in the allowable range for the units of duration that you specify with t3.

t3 - Required

Regular subscription units of duration. Allowable values are:

D — for days; allowable range for p3 is 1 to 90

W — for weeks; allowable range for p3 is 1 to 52

M — for months; allowable range for p3 is 1 to 24

Y — for years; allowable range for p3 is 1 to 5

So the current configuration is a recurring payment for only 1 Month.

I hope that this helps!