Failed to create a subscriber in MailerLite: The app returned, "The given data was invalid.

I’m having all sorts of issues with this one zap.

I’ve a successful zap from ‘new clients’ in Practice better zapped to a new subscriber group in Mailerlite.

I’m trying to set up a new zap from Practice Better when someone confirms a ‘Masterclass booking’ and then then get zapped into a new subscriber group in Mailerlite, but the zap will not work. Even thought it’s just First Name, Last Name and Email… same as the zap that works above.


It’s driving me bonkers this error - The given data was invalid

I’ve tested the PB to Mailerlite is connecting - done working

But it just will not read the data.


correct email to email spot

 correct First name and last Name to spot



10 replies

Userlevel 7
Badge +6

Hi there @Carly I,

Welcome to the Community! 🎉

I have a hunch that the issue here is the mapped email address since it looks like the email address is not valid.

Have you tried publishing the Zap and triggering it to see if the error persists? Also, ensure to check the Zap History to see if you’ll run into the same error.

Additionally, the “Add Subscriber to a Group” action only works for existing subscribers. Changing the action to the “Create or Update Subscriber” could resolve this error as well.

I'll be keeping an eye out for your response!

Confirmed - it’s published and does not work. That email is a test email from Practice better which works on the zap.


Not sure what to do please help if you have a work-around.

Userlevel 7
Badge +6

Hi @Carly I,

I did some digging into this, and it seems like, the SKU field is case sensitive and needs to be an exact match for this built in trigger filter to work as hoped.

Also important to note, Packages and Services are not considered the same thing in Practice Better. Confirmed Package only works for Packages, of course, but the Confirmed Booking trigger will need to be used for Services.

Additionally, have you tried changing the “Add Subscriber to a Group” to “Create or Update Subscriber”?

I'll be keeping an eye out for your response!

Hi, yes the SKU is exact = MCB, Its a booking for a service and I’ve chosen booking trigger for service. Ive also tried create update subscriber and not change to error.

Today I did get around the original error by changing the test email it’s using to one that has booked in the past and the zap works, BUT when I’ve tested this by making a booking - my email does not get added to the subscriber group - yet the test email did. So the zap is still not working



Userlevel 7
Badge +6

Hi @Carly I,

Could you please let me know if there’s any Zap Run in the Zap History and if you’re seeing an error? If so, could you also please send me a screenshot of the Data IN/OUT of the Zap run?

I'll be keeping an eye out for your response!

This post has been edited by a moderator to remove personal information. Please remember that this is a public forum and to remove any sensitive information prior to posting.

So I got the zap to actually work - adding the subscriber to the group using the “Create or Update Subscriber in MailerLite”… and I thought yay! - But then I started to get Zap Run / History emails saying “Required field "Email" (email) is missing.” - which is weird as it was actually working… 

So I went back in and used the Practice Better default email person again (instead of a real exisiting record) and the zap stopped working.

So I went back to the old way and tested it with a real booking and it’s not working again. so d

am frustrating.


Userlevel 7
Badge +6

Hi @Carly I,

I completely understand your frustration here. It looks like the “Confirmed Booking” trigger isn’t returning the Email, First Name, and Last Name data after the Zap runs.  Whenever you see those {{...}} curly braces around entries in the Data In of an action, this means that there is a field mapped there in the Zap Editor, but when the Zap ran live this data was not sent from a previous step.

You might be running into a bug here. I’d recommend reaching out to our Support Team to create a bug report on your behalf or you can reach out Practice Better Support since they’re the ones who owns and maintains their integration in Zapier.

I appreciate your patience and understanding.

SO it’s been a couple of weeks and I’m still not getting any resolution on this issue.

Practice Better say it’s not an issue their end.

Mailerlite say it’s a zapier issue not theirs.

Zapier says there is a bug but they’re busy and to keep continuing the discussion here and track progress?

So I’m not sure what that means at all but I’m at my wits end trying to solve this as the manual work-arounds are getting very difficult for me as I have to manually upload subscribers and now I have an issue where they are not getting subscribed with the opt in - and so no emails get sent to them. Argh.


Anyone have any more things I can try to get the zap to work?


Userlevel 7
Badge +6

Hi @Carly I,

I’m so sorry for the delayed reply.

I’m confident that you’re running into a bug where when the Zap runs the “Confirmed Booking” trigger isn’t returning the customer information that’s why you’re receiving an error in the MailerLite step causing the Zap to fail.

The only workaround that I can think of is by using Webhooks by Zapier as your trigger. However, Webhooks by Zapier is considered an advanced feature, so our support for it may be more limited. Not because we don't want to help, but because APIs can be so different and each request can be so unique. This makes it hard for us to know why the request may be receiving errors or not working as expected. 

I’d recommend reaching out to one of our Zapier Experts to help you setup Webhooks. You can reach our Zapier Experts here:

I’m really sorry for the inconvenience this has caused you. I appreciate your patience and understanding on this matter.

Userlevel 7
Badge +11

Hi again, @Carly I! 🙂

As mentioned in the other thread I’m not entirely sure this is a bug. Would you mind sharing some further screenshots showing a recent run of the Zap that errored in the Zap history?

Specifically I’d like to see the Data Out from the Practice Better trigger as well as the Data In on the MailerLite action that errored. This should help me to better see exactly what the Zap received from Practice Better and attempted to send to MailerLite. And will allow me to check whether there’s any differences in the fields that have been selected in the Zap verses the fields we’re receiving from Practice Better. 

Thanks for your assistance, I looking forward to hearing from you!