We process membership registration/renewal using several civicrm webforms, and at random, clients will be charged twice (so transactions will be processed twice); receipts will be sent twice, and/or there may be a duplicate webform submission. So both errors happen - about 90% goes well, but from my examples
- 2 registrations have 1 submission with 2 receipts
- 2 registrations have 2 submissions with 1 receipt
- 10 registrations have 2 submissions and 2 receipts ('doubleclick')
- 1 registration has 2 submissions and 3 receipts
I see no pattern. I can't find log messages about this.
It seems to happen with all those forms; on each form, the membership type is selected in the civicrm tab of the webform; the membership fee in the membership subtab is unchecked; the contribution amount om the contribution subtab is unchecked. The underlying payment pages have no amounts configured. So civicrm_webform should get the amount from the membership type definition in CiviCRM (right ? looks that way).
We've been going through some updates, and I don't know when this started. Right now the box is shiny and uptodate.
It seems like a timing issue; or forked threads going wild, like communication with the mailserver or payment api. Can that be ?