I had a similar issue recently, with a billing account enabled it was auto cancelled after the trial period ended. Really bad experience.
When you link sendgrid via the cloud launcher, it is linked to your billing account, I was unable to get it reconnected. Had to get intervention from support so that I could re-add sendgrid as new, and create a new user account too. It seems the sendgrid user account is linked to the sendgrid account which is linked to the billing account in GCP. Long story short, don't switch billing accounts if you've added sendgrid via the cloud launcher, which includes being on $300 credit. I found it to be a huge support hole - no one is really responsible for it. I got some help from the cloud launcher team, but obviously GCP trial credits and sendgrid have nothing to do with them. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/ae718b24-0dd5-4139-bba5-7366177ba59f%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
